This is my first attempt at actually making a serious team (and also my first post on Smogon). I have now put in pictures of my team.
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Starmie @ Life Orb
Timid, 252SpA/252 Spe/4 HP
-Hydro Pump
-Thunderbolt
-Ice Beam
-Recover
Starmie makes a great anti-lead as it can outspeed and KO all of the most common ones bar Swampert, which it can't do too much to. Aerodactyl also outspeeds it, but any one of Starmie's moves can take it out. Hydro Pump is chosen for the 2HKO on Metagross, and the accuracy doesn't really bother me. Thunderbolt hits waters other than Swampert, and Ice Beam hits dragons and Breloom/Roserade/Celebi. Recover allows me to shake off LO recoil and stall out weak attackers.
Tyranitar @ Choice Scarf
Jolly, 252Atk/252Spe/4HP
-Stone Edge
-Crunch
-Pursuit
-Earthquake
ScarfTar has been added to deal with a significant Gengar weakness. It also provides a very capable revenge killer against nonscarfed, nonboosted opponents. EdgeQuake for coverage and Crunch for an accurate STAB, plus Pursuit to take down Starmie, Gengar, Celebi, and others. The rest of this moveset is analyzed on the Smogon page for Tyranitar and can really help setting up Metagross.
Heatran @ Leftovers
Timid, 4HP/252Spe/252SpA
-Substitute
-Fire Blast
-Earth Power
-HP Electric
Heatran is a great Scizor counter and can wreak havoc on an unprepared team if he gets a sub up. This is the first team I've used Heatran on, and he works very well. Fire + Ground gives him very good coverage, and HP Electric allows me to get a good hit on Gyarados, who would otherwise wall this set. If Gyarados is weakened enough, Heatran can even KO him.
Celebi @ Leftovers
Timid, 252HP/36Spe/220Def
-Thunder Wave
-HP Fire
-Grass Knot
-Recover
Standard defensive Celebi added per recommendation. A lot of sweepers that would be threatening to my team really hate Thunder Wave, so I decided to use it over Leech Seed, Reflect, or Stealth Rock. HP Fire and Grass Knot allow Celebi to retain a bit of offense, and Recover is self-explanatory on a defensive set.
Gyarados @ Leftovers
Jolly, 252Atk/88HP/168Spe
-Waterfall
-Earthquake
-Taunt
-Dragon Dance
DD Gyarados is insanely powerful. It can come in and force a switch, DD up, and sweep. Leftovers have been added to increase Gyarados's survivability. Waterfall for STAB, Earthquake for coverage. Taunt has been added (per dws93rd' recommendation) to prevent Gyarados from getting phazed. Also, Taunting something like Skarmory or Swampert that can't hurt Gyarados much can allow him to get another DD or two in.
Metagross @ Lum Berry
Adamant, 252Atk/196Spe/60HP
-Agility
-Meteor Mash
-Earthquake
-Explosion
Agiligross. It's one of the best late-game sweepers out there and can outrun most of the metagame with +2 Speed. The given EVs allow it to outrun Scarfed Flygon and Jirachi, which can give it huge problems. Meteor Mash for power, Earthquake for coverage, and Explosion to take something down with me. Gyarados and Skarmory wall this set, but hopefully they've been killed by something earlier. Anyway, Explosion after an Attack boost from Meteor Mash can do a ton of damage to Skarmory, and it OHKOs Gyarados.
How I deal with common Pokemon:
Machamp- It doesn't like getting hit with Meteor Mash, and the Lum Berry on Metagross eliminates DynamicPunch's confusion side effect. If Metagross is dead, Celebi can paralyze No Guard variants and Gyarados can Intimidate it, but Metagross is usually not revealed until late.
Flygon- Scarfed variants are a problem, and my only surefire way of removing a ScarfGon is to hit it with Explosion because of its Ground typing and immunity to Thunder Wave. Gyarados can come in on Earthquake and set up, but is unable to OHKO once it comes back in. NonScarfed Flygon are killed by Starmie's Ice Beam.
Gengar: Tyranitar outspeeds and KOs with either Crunch or Pursuit. If Tyranitar is unavailable, Metagross can hit it with a Meteor Mash or Gyarados can Waterfall if it lacks Thunderbolt.
Heatran: Starmie, Gyarados, or Tyranitar can hit it hard, as can Metagross if it has gotten off an Agility.
Scizor: Celebi can hit it with HP Fire or Heatran can hit it with Fire Blast, not really a problem.
Lucario: Metagross , Gyarados, and Tyranitar can hit it with Earthquake, although Tyranitar must watch out for CCs and Aura Spheres. Celebi can hit it with Hidden Power and Heatran can Fire Blast/ Earth Power in a pinch or from behind a sub.
Tyranitar: Most of my team can hit Tyranitar for SE damage some way or another (EQ, Grass Knot, Hydro Pump, Earth Power, Meteor Mash); however, most of them must watch for a retaliation from Ttar.
Gyarados: Tyranitar can Stone Edge or Starmie can Thunderbolt, but Tyranitar must watch out for Earthquake and Waterfall.
My own Gyarados can Taunt to prevent it getting off a Dragon Dance, but does very little damage back. If Heatran is already out and behind a sub, I can use HP Electric to hurt Gyarados badly.
Jirachi: Depending on the set, different counters can be used. If it's a CM set, Metagross and Tyranitar are the best choices. Gyarados can also be used if it has gotten off a Dance. Scarf sets or paraflinch abuser sets can be countered by the previous choices as well as Heatran and Celebi. Celebi is the best choice for countering a paraflinch set due to Natural Cure (and I guess Starmie could work as well), but Heatran has a 4x resistance to Iron Head, making it an ideal counter to Jirachi locked into Iron Head.
Starmie: Scarfed Starmies are problematic, but Tyranitar can trap them and KO with Pursuit/Crunch or my own Starmie can come in on a Surf/Ice Beam and Thunderbolt. If it's not Scarfed, Tyranitar can still kill it, or Celebi can try to outstall if it lacks Ice Beam.
Metagross: Heatran can Fire Blast it, but needs to watch out for Earthquake. My physical attackers can Earthquake, but Metagross and Tyranitar are weak to common moves, so Gyarados is the best counter if it lacks Thunderpunch. Celebi can hit it with HP Fire, but it's a weak hit on a strong Pokemon and should be used only as a last resort. Also, Hydro Pump from Starmie 2HKOs lead Metagross.
Infernape: Gyarados is the most reliable counter, but anything except for Celebi works, really. Tyranitar and Heatran just need to watch out for CCs, Mach Punch, and Vacuum Wave. Starmie could get hit by a lucky U-Turn and Metagross doesn't like Fire attacks, but Infernape loses to this team.
Blissey: Metagross or Gyarados, take your pick. Metagross can absorb status, but hates paralysis if Meteor Mash misses or something. Gyarados also hates status, but can set up and sweep a few Pokemon before dying to Toxic if he must.
Azelf: Starmie does quite well against lead Azelf and doesn't mind getting Tricked. Tyranitar can also take a Trick and OHKO with Pursuit.
Swampert: Doesn't really like Starmie's Hydro Pumps, but he can take a few. Celebi can hit it with Grass Knot or Heatran can kill it with HP Grass.
Breloom: Take the Spore, and then Ice Beam/Fire Blast/HP Fire. I hate this mushroom-headed @*#@ more than words can possibly describe, and will never, ever use it on a team of mine.
Gliscor: Dies easily enough to an Ice Beam or Waterfall. I rarely see Gliscor anyway.
Vaporeon: Thunderbolt will kill it in 2 hits, as long as there's no Wish/Protect going on. Gyarados can set up on those without HP Electric, and Heatran can sub up while it recovers and hit it with HP Grass. Celebi's Grass Knot has bad BP, but Vaporeon can't do much back to Celebi due to Natural Cure and Recover.
Jolteon: Metagross and Tyranitar can Earthquake and Heatran can Earth Power. Gyarados needs to watch out, though.
EDIT LIST: changed celebi to defensive, gave gyarados leftovers instead of wacan berry, changed flamethrower to thunderbolt on tyranitar. also added pictures.
changed stone edge on gyarados to taunt.
changed metagross's EVs
changed MixTar to ScarfTar
added threat list
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Starmie @ Life Orb
Timid, 252SpA/252 Spe/4 HP
-Hydro Pump
-Thunderbolt
-Ice Beam
-Recover
Starmie makes a great anti-lead as it can outspeed and KO all of the most common ones bar Swampert, which it can't do too much to. Aerodactyl also outspeeds it, but any one of Starmie's moves can take it out. Hydro Pump is chosen for the 2HKO on Metagross, and the accuracy doesn't really bother me. Thunderbolt hits waters other than Swampert, and Ice Beam hits dragons and Breloom/Roserade/Celebi. Recover allows me to shake off LO recoil and stall out weak attackers.

Tyranitar @ Choice Scarf
Jolly, 252Atk/252Spe/4HP
-Stone Edge
-Crunch
-Pursuit
-Earthquake
ScarfTar has been added to deal with a significant Gengar weakness. It also provides a very capable revenge killer against nonscarfed, nonboosted opponents. EdgeQuake for coverage and Crunch for an accurate STAB, plus Pursuit to take down Starmie, Gengar, Celebi, and others. The rest of this moveset is analyzed on the Smogon page for Tyranitar and can really help setting up Metagross.

Heatran @ Leftovers
Timid, 4HP/252Spe/252SpA
-Substitute
-Fire Blast
-Earth Power
-HP Electric
Heatran is a great Scizor counter and can wreak havoc on an unprepared team if he gets a sub up. This is the first team I've used Heatran on, and he works very well. Fire + Ground gives him very good coverage, and HP Electric allows me to get a good hit on Gyarados, who would otherwise wall this set. If Gyarados is weakened enough, Heatran can even KO him.

Celebi @ Leftovers
Timid, 252HP/36Spe/220Def
-Thunder Wave
-HP Fire
-Grass Knot
-Recover
Standard defensive Celebi added per recommendation. A lot of sweepers that would be threatening to my team really hate Thunder Wave, so I decided to use it over Leech Seed, Reflect, or Stealth Rock. HP Fire and Grass Knot allow Celebi to retain a bit of offense, and Recover is self-explanatory on a defensive set.

Gyarados @ Leftovers
Jolly, 252Atk/88HP/168Spe
-Waterfall
-Earthquake
-Taunt
-Dragon Dance
DD Gyarados is insanely powerful. It can come in and force a switch, DD up, and sweep. Leftovers have been added to increase Gyarados's survivability. Waterfall for STAB, Earthquake for coverage. Taunt has been added (per dws93rd' recommendation) to prevent Gyarados from getting phazed. Also, Taunting something like Skarmory or Swampert that can't hurt Gyarados much can allow him to get another DD or two in.

Metagross @ Lum Berry
Adamant, 252Atk/196Spe/60HP
-Agility
-Meteor Mash
-Earthquake
-Explosion
Agiligross. It's one of the best late-game sweepers out there and can outrun most of the metagame with +2 Speed. The given EVs allow it to outrun Scarfed Flygon and Jirachi, which can give it huge problems. Meteor Mash for power, Earthquake for coverage, and Explosion to take something down with me. Gyarados and Skarmory wall this set, but hopefully they've been killed by something earlier. Anyway, Explosion after an Attack boost from Meteor Mash can do a ton of damage to Skarmory, and it OHKOs Gyarados.
How I deal with common Pokemon:
Machamp- It doesn't like getting hit with Meteor Mash, and the Lum Berry on Metagross eliminates DynamicPunch's confusion side effect. If Metagross is dead, Celebi can paralyze No Guard variants and Gyarados can Intimidate it, but Metagross is usually not revealed until late.
Flygon- Scarfed variants are a problem, and my only surefire way of removing a ScarfGon is to hit it with Explosion because of its Ground typing and immunity to Thunder Wave. Gyarados can come in on Earthquake and set up, but is unable to OHKO once it comes back in. NonScarfed Flygon are killed by Starmie's Ice Beam.
Gengar: Tyranitar outspeeds and KOs with either Crunch or Pursuit. If Tyranitar is unavailable, Metagross can hit it with a Meteor Mash or Gyarados can Waterfall if it lacks Thunderbolt.
Heatran: Starmie, Gyarados, or Tyranitar can hit it hard, as can Metagross if it has gotten off an Agility.
Scizor: Celebi can hit it with HP Fire or Heatran can hit it with Fire Blast, not really a problem.
Lucario: Metagross , Gyarados, and Tyranitar can hit it with Earthquake, although Tyranitar must watch out for CCs and Aura Spheres. Celebi can hit it with Hidden Power and Heatran can Fire Blast/ Earth Power in a pinch or from behind a sub.
Tyranitar: Most of my team can hit Tyranitar for SE damage some way or another (EQ, Grass Knot, Hydro Pump, Earth Power, Meteor Mash); however, most of them must watch for a retaliation from Ttar.
Gyarados: Tyranitar can Stone Edge or Starmie can Thunderbolt, but Tyranitar must watch out for Earthquake and Waterfall.
My own Gyarados can Taunt to prevent it getting off a Dragon Dance, but does very little damage back. If Heatran is already out and behind a sub, I can use HP Electric to hurt Gyarados badly.
Jirachi: Depending on the set, different counters can be used. If it's a CM set, Metagross and Tyranitar are the best choices. Gyarados can also be used if it has gotten off a Dance. Scarf sets or paraflinch abuser sets can be countered by the previous choices as well as Heatran and Celebi. Celebi is the best choice for countering a paraflinch set due to Natural Cure (and I guess Starmie could work as well), but Heatran has a 4x resistance to Iron Head, making it an ideal counter to Jirachi locked into Iron Head.
Starmie: Scarfed Starmies are problematic, but Tyranitar can trap them and KO with Pursuit/Crunch or my own Starmie can come in on a Surf/Ice Beam and Thunderbolt. If it's not Scarfed, Tyranitar can still kill it, or Celebi can try to outstall if it lacks Ice Beam.
Metagross: Heatran can Fire Blast it, but needs to watch out for Earthquake. My physical attackers can Earthquake, but Metagross and Tyranitar are weak to common moves, so Gyarados is the best counter if it lacks Thunderpunch. Celebi can hit it with HP Fire, but it's a weak hit on a strong Pokemon and should be used only as a last resort. Also, Hydro Pump from Starmie 2HKOs lead Metagross.
Infernape: Gyarados is the most reliable counter, but anything except for Celebi works, really. Tyranitar and Heatran just need to watch out for CCs, Mach Punch, and Vacuum Wave. Starmie could get hit by a lucky U-Turn and Metagross doesn't like Fire attacks, but Infernape loses to this team.
Blissey: Metagross or Gyarados, take your pick. Metagross can absorb status, but hates paralysis if Meteor Mash misses or something. Gyarados also hates status, but can set up and sweep a few Pokemon before dying to Toxic if he must.
Azelf: Starmie does quite well against lead Azelf and doesn't mind getting Tricked. Tyranitar can also take a Trick and OHKO with Pursuit.
Swampert: Doesn't really like Starmie's Hydro Pumps, but he can take a few. Celebi can hit it with Grass Knot or Heatran can kill it with HP Grass.
Breloom: Take the Spore, and then Ice Beam/Fire Blast/HP Fire. I hate this mushroom-headed @*#@ more than words can possibly describe, and will never, ever use it on a team of mine.
Gliscor: Dies easily enough to an Ice Beam or Waterfall. I rarely see Gliscor anyway.
Vaporeon: Thunderbolt will kill it in 2 hits, as long as there's no Wish/Protect going on. Gyarados can set up on those without HP Electric, and Heatran can sub up while it recovers and hit it with HP Grass. Celebi's Grass Knot has bad BP, but Vaporeon can't do much back to Celebi due to Natural Cure and Recover.
Jolteon: Metagross and Tyranitar can Earthquake and Heatran can Earth Power. Gyarados needs to watch out, though.
EDIT LIST: changed celebi to defensive, gave gyarados leftovers instead of wacan berry, changed flamethrower to thunderbolt on tyranitar. also added pictures.
changed stone edge on gyarados to taunt.
changed metagross's EVs
changed MixTar to ScarfTar
added threat list