I've been playing with this Hail team for VGC 2012 for a few weeks now, and it's had a fair amount of success, however, it could definitely do with some improvements.
The Team
Abomasnow (M) @ Occa Berry
Trait: Snow Warning
EVs: 252 HP / 4 Atk / 252 SAtk
Quiet Nature (+SAtk, -Spd)
- Blizzard
- Giga Drain
- Ice Shard
- Protect
Without Abomasnow, this team wouldn't even be a Hail team. I chose bulky spread over Scarfed as I really enjoy the utility of Protect. Blizzard and Giga Drain are powerful Special STABs, Blizzard being able to hit both opponents with a chance to freeze, and Giga Drain restoring HP. Ice Shard is priority, used as a last ditch move when Abomasnow is nearly dead, or to quickly finish one opponent off. Occa Berry lets Abomasnow take at least one Fire-type attack and still get a hit off. Max HP and SpA EVs are to maximise bulk and offence, with the last 4 EVs going into Atk to give Ice Shard a bit more power. A Quiet nature and 0 Spd IVs are to outslow other weather users at the start of a battle and get my weather up and running.
Mamoswine (M) @ Life Orb
Trait: Oblivious
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Ice Shard
- Icicle Spear
- Rock Slide
- Protect
Mamoswine is my physical Hail abuser. Ice Shard is a strong priority STAB, being able to do serious damage to anything weak to it. Icicle Spear is Mamoswine's other Ice STAB, doing hefty damage and being able to break Sturdy and Focus Sash. For the 3rd attack, I went with Rock Slide over Earthquake for 2 reasons; the chance to flinch is really nice, and Mamoswine is usually sent out first with Abomasnow, and I really hate damaging my own team mates, because that's screwed me over a few times in the past. Max Atk and Spd with Jolly nature and Life Orb to dish out as much damage as possible as quickly as possible.
Latios (M) @ White Herb
Trait: Levitate
EVs: 4 HP / 4 Def / 248 SAtk / 4 SDef / 248 Spd
Timid Nature (+Spd, -Atk)
- Draco Meteor
- Psyshock
- Surf
- Protect
White Herb Latios is one of my favourite things in the VGC 2012 metagame, being able to fire off a power Draco Meteor, and still able to dish out damage without having to switch. The EVs and Nature are taken from Smogon's page for Latios. Draco Meteor is Latios' main weapon of choice, doing severe damage to anything that doesn't resist it. I've chosen Psyshock over Psychic to hit specially defensive opponents, and Surf is to round off the set, hitting Rock, Ground, and Fire types super effectively.
Froslass (F) @ Focus Sash
Trait: Snow Cloak
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Blizzard
- Shadow Ball
- Destiny Bond
- Protect
Froslass is my other Hail abuser, this time being specially offensive. With a Focus Sash, Froslass can survive a hit with at least one HP left, and if I think the opponent is going to attack Froslass the next turn, I use Destiny Bond to take the opponent down with me. And if that doesn't work, due to either my opponent not attacking, or missing due to Snow Cloak, they get scared of the Destiny Bond and focus their energy on Froslass' partner. Blizzard and Shadow Ball are Froslass' dual STAB, Blizzard hitting both opponents with a chance to freeze, and Shadow Ball hitting Ghost and Psychic types and potentially lowering SpD. And max SpA and Spd with a Timid nature are for dishing out as much damage as possible before having to Destiny Bond.
Rotom-W @ Electric Gem
Trait: Levitate
EVs: 252 HP / 252 SAtk / 4 SDef
Modest Nature (+SAtk, -Atk)
- Thunderbolt
- Hydro Pump
- Hidden Power [Fire]
- Protect
Another Pokemon I love to run in VGCs. Rotom-W with an Electric Gem can do hefty damage to Rain teams, with an Electic Gem-boosted Thunderbolt being able to easily OHKO defensive Politoed. Hydro Pump is Rotom's other STAB, doing nice damage to many Pokemon, and Hidden Power Fire is to remedy the lack of options against Steel Pokemon. Max HP and SpA with a Modest nature are for maximum bulk and offensive power, with the last 4 EVs going to SpD so Rotom can take Special moves a tad better than what it would otherwise.
Hitmontop (M) @ Sitrus Berry
Trait: Intimidate
EVs: 252 HP / 252 Atk / 4 SDef
Adamant Nature (+Atk, -SAtk)
- Fake Out
- Close Combat
- Sucker Punch
- Detect
Hitmontop is a bit of a utility Pokemon, being very bulky and weakening the strength of physical opponents with Intimidate. Fake Out is a necessity on Hitmontop, breaking Focus Sash and Sturdy, as well as stopping one opposing Pokemon from doing anything for a turn. Close Combat is Hitmontop's STAB attack, doing lots of damage to unresisted hits, and a lot of damage to even Chople Berry Tyranitar, which is a pretty big threat to this team, and Sucker Punch is an option for getting the jump on an attacking opponent, which can potentially OHKO things like Gengar and Latios. Max HP and Atk with an Adamant nature for bulk and power, and a Sitrus berry is to keep Hitmontop healthy.
Overall, I'm very happy with how this team works. I've won most of the battles I've had, but it still has a few issues. I have a bit of trouble with Sand teams due them being a good counter to Hail in general.
The Team

Abomasnow (M) @ Occa Berry
Trait: Snow Warning
EVs: 252 HP / 4 Atk / 252 SAtk
Quiet Nature (+SAtk, -Spd)
- Blizzard
- Giga Drain
- Ice Shard
- Protect
Without Abomasnow, this team wouldn't even be a Hail team. I chose bulky spread over Scarfed as I really enjoy the utility of Protect. Blizzard and Giga Drain are powerful Special STABs, Blizzard being able to hit both opponents with a chance to freeze, and Giga Drain restoring HP. Ice Shard is priority, used as a last ditch move when Abomasnow is nearly dead, or to quickly finish one opponent off. Occa Berry lets Abomasnow take at least one Fire-type attack and still get a hit off. Max HP and SpA EVs are to maximise bulk and offence, with the last 4 EVs going into Atk to give Ice Shard a bit more power. A Quiet nature and 0 Spd IVs are to outslow other weather users at the start of a battle and get my weather up and running.

Mamoswine (M) @ Life Orb
Trait: Oblivious
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Ice Shard
- Icicle Spear
- Rock Slide
- Protect
Mamoswine is my physical Hail abuser. Ice Shard is a strong priority STAB, being able to do serious damage to anything weak to it. Icicle Spear is Mamoswine's other Ice STAB, doing hefty damage and being able to break Sturdy and Focus Sash. For the 3rd attack, I went with Rock Slide over Earthquake for 2 reasons; the chance to flinch is really nice, and Mamoswine is usually sent out first with Abomasnow, and I really hate damaging my own team mates, because that's screwed me over a few times in the past. Max Atk and Spd with Jolly nature and Life Orb to dish out as much damage as possible as quickly as possible.

Latios (M) @ White Herb
Trait: Levitate
EVs: 4 HP / 4 Def / 248 SAtk / 4 SDef / 248 Spd
Timid Nature (+Spd, -Atk)
- Draco Meteor
- Psyshock
- Surf
- Protect
White Herb Latios is one of my favourite things in the VGC 2012 metagame, being able to fire off a power Draco Meteor, and still able to dish out damage without having to switch. The EVs and Nature are taken from Smogon's page for Latios. Draco Meteor is Latios' main weapon of choice, doing severe damage to anything that doesn't resist it. I've chosen Psyshock over Psychic to hit specially defensive opponents, and Surf is to round off the set, hitting Rock, Ground, and Fire types super effectively.

Froslass (F) @ Focus Sash
Trait: Snow Cloak
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Blizzard
- Shadow Ball
- Destiny Bond
- Protect
Froslass is my other Hail abuser, this time being specially offensive. With a Focus Sash, Froslass can survive a hit with at least one HP left, and if I think the opponent is going to attack Froslass the next turn, I use Destiny Bond to take the opponent down with me. And if that doesn't work, due to either my opponent not attacking, or missing due to Snow Cloak, they get scared of the Destiny Bond and focus their energy on Froslass' partner. Blizzard and Shadow Ball are Froslass' dual STAB, Blizzard hitting both opponents with a chance to freeze, and Shadow Ball hitting Ghost and Psychic types and potentially lowering SpD. And max SpA and Spd with a Timid nature are for dishing out as much damage as possible before having to Destiny Bond.

Rotom-W @ Electric Gem
Trait: Levitate
EVs: 252 HP / 252 SAtk / 4 SDef
Modest Nature (+SAtk, -Atk)
- Thunderbolt
- Hydro Pump
- Hidden Power [Fire]
- Protect
Another Pokemon I love to run in VGCs. Rotom-W with an Electric Gem can do hefty damage to Rain teams, with an Electic Gem-boosted Thunderbolt being able to easily OHKO defensive Politoed. Hydro Pump is Rotom's other STAB, doing nice damage to many Pokemon, and Hidden Power Fire is to remedy the lack of options against Steel Pokemon. Max HP and SpA with a Modest nature are for maximum bulk and offensive power, with the last 4 EVs going to SpD so Rotom can take Special moves a tad better than what it would otherwise.

Hitmontop (M) @ Sitrus Berry
Trait: Intimidate
EVs: 252 HP / 252 Atk / 4 SDef
Adamant Nature (+Atk, -SAtk)
- Fake Out
- Close Combat
- Sucker Punch
- Detect
Hitmontop is a bit of a utility Pokemon, being very bulky and weakening the strength of physical opponents with Intimidate. Fake Out is a necessity on Hitmontop, breaking Focus Sash and Sturdy, as well as stopping one opposing Pokemon from doing anything for a turn. Close Combat is Hitmontop's STAB attack, doing lots of damage to unresisted hits, and a lot of damage to even Chople Berry Tyranitar, which is a pretty big threat to this team, and Sucker Punch is an option for getting the jump on an attacking opponent, which can potentially OHKO things like Gengar and Latios. Max HP and Atk with an Adamant nature for bulk and power, and a Sitrus berry is to keep Hitmontop healthy.
Overall, I'm very happy with how this team works. I've won most of the battles I've had, but it still has a few issues. I have a bit of trouble with Sand teams due them being a good counter to Hail in general.