After fooling around with a mono-poison team, I found that there were some things it simply could not handle. However, a regular team is too boring, so I decided on a gimmick that was way more effective: mono-water.
Gyarados @ leftovers
Intimidate
Adamant, 216 HP, 16 AT, 176 DF, 100 Spd
Dragon Dance
Taunt
Waterfall
Ice Fang
Standard Bulky Gyara. Possibly the best starter in the game, and with Intimidate and Grass neutrality, this guy is a must on a mono-water team. That said, electric still rapes him, so I have...
Swampert @ leftovers
Torrent
Relaxed, 240HP, 216 DF, 52 SpA
Earthquake
Hydro Pump
Ice Beam
Stealth Rock
... who resists rock AND is immune to electric:) Again, you simply can't have a mono-water team without arguably the best stealth-rocker in the game, in addition to a premier tank.
Vaporeon @ leftovers
Water Absorb
Bold, 188 HP, 252 DF, 68 SpA
Wish
Protect
Surf
Ice Beam
I know, so far these are all standard sets, but they're standard cause they work so well. Gives my team valuable Wish support, scouts stuff with protect, and has decent special attack. Also, Grass Knot is only 60 BP on it, for whatever that's worth.
Kingdra @ Damp Rock
Swift Swim
Modest, 120 HP, 252 SpA, 136 Spd
Rain Dance
Surf
Ice Beam
HP Electric
This thing usually manages to get Rain Dance up at least once in a match, and MAN is it useful. Standard RD Special Kingdra, though it loses to Blissey. Not to worry though...
Azumarill @ Choice Band
Huge Power
Adamant, 252 AT, 252 HP, 6 DF
Waterfall
Aqua Jet
Focus Punch
Brick Break
My main physical attacker. I know the coverage is crap with 2 water/fighting moves, but I think all these moves are needed sans focus punch, which is filler really. Aqua Jet in the rain 2HKOs Gyarados assuming no intimidate. Too good.
Suicune @ Leftovers
Pressure
Bold, 252 HP, 252 DF, 6 SpA
Surf
Calm Mind
Roar
Rest
Ah, good ol' Calmcune. Psuedo-hazer, stalling tank, and status absorber. Is there anything it can't do? What, damage Water Absorb pokes? Oh.... Well luckily pokemon isn't a 1v1 game.
There you have it. I haven't lost once with this team, but I'm sure it can be beaten pretty well. I also have a problem with Grass moves, seeing as how gyara/kingdra are both only neutral and can't keep coming in.
I was also considering tentacruel for rapid spin/toxic spike absorb, but I can't bear to replace any of these guys without good reason. I imagine starmie would be incredibly useful too, but who would he replace?
Gyarados @ leftovers
Intimidate
Adamant, 216 HP, 16 AT, 176 DF, 100 Spd
Dragon Dance
Taunt
Waterfall
Ice Fang
Standard Bulky Gyara. Possibly the best starter in the game, and with Intimidate and Grass neutrality, this guy is a must on a mono-water team. That said, electric still rapes him, so I have...
Swampert @ leftovers
Torrent
Relaxed, 240HP, 216 DF, 52 SpA
Earthquake
Hydro Pump
Ice Beam
Stealth Rock
... who resists rock AND is immune to electric:) Again, you simply can't have a mono-water team without arguably the best stealth-rocker in the game, in addition to a premier tank.
Vaporeon @ leftovers
Water Absorb
Bold, 188 HP, 252 DF, 68 SpA
Wish
Protect
Surf
Ice Beam
I know, so far these are all standard sets, but they're standard cause they work so well. Gives my team valuable Wish support, scouts stuff with protect, and has decent special attack. Also, Grass Knot is only 60 BP on it, for whatever that's worth.
Kingdra @ Damp Rock
Swift Swim
Modest, 120 HP, 252 SpA, 136 Spd
Rain Dance
Surf
Ice Beam
HP Electric
This thing usually manages to get Rain Dance up at least once in a match, and MAN is it useful. Standard RD Special Kingdra, though it loses to Blissey. Not to worry though...
Azumarill @ Choice Band
Huge Power
Adamant, 252 AT, 252 HP, 6 DF
Waterfall
Aqua Jet
Focus Punch
Brick Break
My main physical attacker. I know the coverage is crap with 2 water/fighting moves, but I think all these moves are needed sans focus punch, which is filler really. Aqua Jet in the rain 2HKOs Gyarados assuming no intimidate. Too good.
Suicune @ Leftovers
Pressure
Bold, 252 HP, 252 DF, 6 SpA
Surf
Calm Mind
Roar
Rest
Ah, good ol' Calmcune. Psuedo-hazer, stalling tank, and status absorber. Is there anything it can't do? What, damage Water Absorb pokes? Oh.... Well luckily pokemon isn't a 1v1 game.
There you have it. I haven't lost once with this team, but I'm sure it can be beaten pretty well. I also have a problem with Grass moves, seeing as how gyara/kingdra are both only neutral and can't keep coming in.
I was also considering tentacruel for rapid spin/toxic spike absorb, but I can't bear to replace any of these guys without good reason. I imagine starmie would be incredibly useful too, but who would he replace?