I'm in a minority of players who think that Hail happens to be the best weather out there. Hopefully the new games will buff the hail mechanics a bit but for now they work just fine. This team's main focus is to ensure Hail is always on the field, if not for my Pokemon just to shut down other weather teams. Ice Sharding is another strength. OU is just littered with Dragon types waiting to be OHKOd or 2HKOd.
The Roster:
President Abomasnow@ Focus Sash
Ability: Snow Warning
Jolly Nature. Evs: 252 Speed, 252 Attack, 4 HP.
-Ice Shard
-Swords Dance
-Seed Bomb
-Earthquake
Abomasnow isn't prez of this team for nothing. Ice Shard is in my humble opinion one of the best moves in the game, and it turns Abomasnow into a pretty potent attacker. Jolly Nature and max speed investment usually lets it move before Non-scarfed Heatran people love to send out against Abomasnow, usually 1HKOing with EQ. Earthquake+Focus Sash+Hail damage+Ice Shard will usually knock out opposing Ninetales as well, devastating sun teams that would otherwise plow through. Chansey is another frequent switch-in, expecting Blizzard. Chansey gives it plenty of time to Swords Dance up and go for a sweep.
After a Swords Dance this guy is surprisingly powerful. Seed Bomb ensures Abomasnow doesn't go breaking his own Focus Sash as he would with Wood Hammer. Jellicent works very well with Abomasnow, absorbing Fake Outs and Fire attacks that would use up the Focus Sash. Jellicent can also Water Absorb/take Focus Blasts and change the weather back to Hail against Politoed.
Mamoswine@ Leftovers
Ability: Snow Cloak
Adamant Nature. Evs: 6 HP, 252 Attack, 152 SpD, 100 Speed.
-EQ
-Ice Shard
-Stone Edge
-Curse
Mamoswine is unarguably a beast. Curse makes it even beastlier, and actually able to withstand a hit. The strategy is simple: Switch into an Electric attack or something non-threatening (Jellicent can usually bait an Electric attack) and Curse on the switch. Ice Shard becomes immensely powerful after a Curse, bypassing the Speed drop. After a Curse or 2, Bullet Punches are a lot less threatening and EQs are much more terrifying. Stone Edge is mainly for coverage.
This used to be a Jolly+Life Orb set, but I find the tank Mamoswine to be much more useful, especially if saved for later in the battle. If a Curse isn't possible, Mamoswine's Attack is 394 anyway. Mamoswine is also great because he can function well against opposing Sand Stream teams.
Mow Rotom@ Choice Scarf
Ability: Levitate
Timid Nature: EVs: 6 HP, 252 SpA, 252 Speed
-Leaf Storm
-Thunderbolt
-Volt Switch
-Hidden Power [Fire]
Mow Rotom is my answer to Rotom-W and Gastrodon, who are both otherwise very annoying. Mow Rotom is also boss at Volt Switching. Mow Rotom's only downside is it brings another unfortunate Fire weakness to the team, but it's High Speed is very valuable.
I used to use Rotom-F and spam Blizzard but Rotom-W became too much of a hassle.
Espeon@ Leftovers
Ability: Magic Bounce
Timid Nature. Evs: 6 HP, 252 SpA, 252 Speed
-Baton Pass
-Calm Mind
-Psychic
-Hidden Power [Fire]
Magic Bounce Espeon is pretty important to this team. Entry hazards will take the edge off of this team pretty quickly. Espeon also helps out the Ice types on this team when it comes to Fighting attacks. It also easily removes Conkeldurr and Scizor (Espeon can usually take one Bullet Punch and retailiate with HP Fire). Jellicent and Rotom also don't mind Calm Mind boosts Espeon can pass around.
Bronzong @ Iron Ball
Ability: Heatproof
Brave Nature. EVs: 106 HP, 252 Attack, 150 SpD. (No Speed IVs).
-Gyro Ball
-Earthquake
-Skill Swap
-Trick
Yeah, you read that right-Heatproof. With too many fire weaknesses on this team and too little Ground weaknesses, Heatproof is a fantastic ability. It also is somewhat sneaky. Everyone assumes I'm running Levitate (even more important to keep Spikes off the field), so they attack with Fire attacks. By that time it's too late. It also lets me hold an Iron Ball to buff up Gyro Ball's base power, or more preferably, Tricking onto opposing Sweepers or Skarmory.
The real fun with this Bronzong is Skill Swap. Sigilyph being annoying not taking any damage? Skill Swap makes it take Hail and Burn/Toxic Damage. Azumarill a nuisance? Bronzong really likes having Huge Power. The possibilities are really endless. Heatproof is also a pretty useless ability to have Swapped onto you. This Bronzong is just fun and an all-around great Pokemon. It's Steel/Psychic typing is also a blessing.
Jellicent@ Leftovers/Icy Rock
Ability: Water Absorb
-Surf
-Will-O-Wisp
-Recover
-Hail
Jellicent's typing is just a godsend for this team. Resistance to Bug/Steel/Fire and an immunity to Fighting are very much appreciated. It also stands up to Politoed quite nicely, barring Toxic. Haven't really settled on an EV spread or Nature-constantly experimenting.
I carry Hail on Jellicent as a back up to keep the weather wars running in my favor. This set used to have Scald/Blizzard instead of Surf/Will-o-Wisp. Blizzard was a nice surprise factor with Hail, but Scald's burning chances just never really worked out for me. Surf is also much better in terms of damage output. Jellicent is even better if I can pass it a Calm Mind boost or two.
Occasional Sub:
Medicham@ Choice Scarf
Ability: Huge Power
Adamant Nature. Evs: 6 HP, 252 Attack, 252 Speed.
-Hi Jump Kick
-Psycho Cut
-Fire Punch
-Thunder Punch
Can anyone say "beast"?. Once ghost-types are gone it's time to start Hi Jump Kickin'. Just completely tears wholes in teams, even fighting resists. Psycho Cut is also good bait for Gengars expecting to switch into a Hi Jump Kick.
Any thoughts and suggestions would be appreciated. :)
The Roster:

Ability: Snow Warning
Jolly Nature. Evs: 252 Speed, 252 Attack, 4 HP.
-Ice Shard
-Swords Dance
-Seed Bomb
-Earthquake
Abomasnow isn't prez of this team for nothing. Ice Shard is in my humble opinion one of the best moves in the game, and it turns Abomasnow into a pretty potent attacker. Jolly Nature and max speed investment usually lets it move before Non-scarfed Heatran people love to send out against Abomasnow, usually 1HKOing with EQ. Earthquake+Focus Sash+Hail damage+Ice Shard will usually knock out opposing Ninetales as well, devastating sun teams that would otherwise plow through. Chansey is another frequent switch-in, expecting Blizzard. Chansey gives it plenty of time to Swords Dance up and go for a sweep.
After a Swords Dance this guy is surprisingly powerful. Seed Bomb ensures Abomasnow doesn't go breaking his own Focus Sash as he would with Wood Hammer. Jellicent works very well with Abomasnow, absorbing Fake Outs and Fire attacks that would use up the Focus Sash. Jellicent can also Water Absorb/take Focus Blasts and change the weather back to Hail against Politoed.

Mamoswine@ Leftovers
Ability: Snow Cloak
Adamant Nature. Evs: 6 HP, 252 Attack, 152 SpD, 100 Speed.
-EQ
-Ice Shard
-Stone Edge
-Curse
Mamoswine is unarguably a beast. Curse makes it even beastlier, and actually able to withstand a hit. The strategy is simple: Switch into an Electric attack or something non-threatening (Jellicent can usually bait an Electric attack) and Curse on the switch. Ice Shard becomes immensely powerful after a Curse, bypassing the Speed drop. After a Curse or 2, Bullet Punches are a lot less threatening and EQs are much more terrifying. Stone Edge is mainly for coverage.
This used to be a Jolly+Life Orb set, but I find the tank Mamoswine to be much more useful, especially if saved for later in the battle. If a Curse isn't possible, Mamoswine's Attack is 394 anyway. Mamoswine is also great because he can function well against opposing Sand Stream teams.

Mow Rotom@ Choice Scarf
Ability: Levitate
Timid Nature: EVs: 6 HP, 252 SpA, 252 Speed
-Leaf Storm
-Thunderbolt
-Volt Switch
-Hidden Power [Fire]
Mow Rotom is my answer to Rotom-W and Gastrodon, who are both otherwise very annoying. Mow Rotom is also boss at Volt Switching. Mow Rotom's only downside is it brings another unfortunate Fire weakness to the team, but it's High Speed is very valuable.
I used to use Rotom-F and spam Blizzard but Rotom-W became too much of a hassle.

Espeon@ Leftovers
Ability: Magic Bounce
Timid Nature. Evs: 6 HP, 252 SpA, 252 Speed
-Baton Pass
-Calm Mind
-Psychic
-Hidden Power [Fire]
Magic Bounce Espeon is pretty important to this team. Entry hazards will take the edge off of this team pretty quickly. Espeon also helps out the Ice types on this team when it comes to Fighting attacks. It also easily removes Conkeldurr and Scizor (Espeon can usually take one Bullet Punch and retailiate with HP Fire). Jellicent and Rotom also don't mind Calm Mind boosts Espeon can pass around.

Bronzong @ Iron Ball
Ability: Heatproof
Brave Nature. EVs: 106 HP, 252 Attack, 150 SpD. (No Speed IVs).
-Gyro Ball
-Earthquake
-Skill Swap
-Trick
Yeah, you read that right-Heatproof. With too many fire weaknesses on this team and too little Ground weaknesses, Heatproof is a fantastic ability. It also is somewhat sneaky. Everyone assumes I'm running Levitate (even more important to keep Spikes off the field), so they attack with Fire attacks. By that time it's too late. It also lets me hold an Iron Ball to buff up Gyro Ball's base power, or more preferably, Tricking onto opposing Sweepers or Skarmory.
The real fun with this Bronzong is Skill Swap. Sigilyph being annoying not taking any damage? Skill Swap makes it take Hail and Burn/Toxic Damage. Azumarill a nuisance? Bronzong really likes having Huge Power. The possibilities are really endless. Heatproof is also a pretty useless ability to have Swapped onto you. This Bronzong is just fun and an all-around great Pokemon. It's Steel/Psychic typing is also a blessing.

Jellicent@ Leftovers/Icy Rock
Ability: Water Absorb
-Surf
-Will-O-Wisp
-Recover
-Hail
Jellicent's typing is just a godsend for this team. Resistance to Bug/Steel/Fire and an immunity to Fighting are very much appreciated. It also stands up to Politoed quite nicely, barring Toxic. Haven't really settled on an EV spread or Nature-constantly experimenting.
I carry Hail on Jellicent as a back up to keep the weather wars running in my favor. This set used to have Scald/Blizzard instead of Surf/Will-o-Wisp. Blizzard was a nice surprise factor with Hail, but Scald's burning chances just never really worked out for me. Surf is also much better in terms of damage output. Jellicent is even better if I can pass it a Calm Mind boost or two.
Occasional Sub:

Medicham@ Choice Scarf
Ability: Huge Power
Adamant Nature. Evs: 6 HP, 252 Attack, 252 Speed.
-Hi Jump Kick
-Psycho Cut
-Fire Punch
-Thunder Punch
Can anyone say "beast"?. Once ghost-types are gone it's time to start Hi Jump Kickin'. Just completely tears wholes in teams, even fighting resists. Psycho Cut is also good bait for Gengars expecting to switch into a Hi Jump Kick.
Any thoughts and suggestions would be appreciated. :)