Abomasnow is a good point to start from. I'd rather have it be a Choice Scarf revenge-killer, killing Pokémon expecting speed help from their weather. Some people prefer it bulky with Leech Seed and stuff, so it's up to you, really. Try both and see waht fits your team best.
Walrein is the next step. Every respectable hail team has a Walrein on it, and if you are unaware of its infamous set "StallRein", then you better read few articles on hail teams. Smogon is nice for that.
Alternatively, new Pokes get Ice Body from Dream World this gen, so you could try those.
Usually, Hail teams resolve around passive damage from Hail but also from entry hazards. Choosing good Pokémon to set up entry hazards as well as spinning them away (as most ice-types are sr-weak) would be your objective.
Stealth Rock users:
Mamoswine: Immediately springs to mind as a neat user of SR in Hail Team, having access to the ever-useful Snow Cloak and dealing tons of damage with Earthquake and Icicle Crash, Mamoswine has plenty of opportunities to use Stealth Rock during the switches it forces. And, once its done, it is far from a dead weight.
Empoleon: Nice resistances, pairs up pretty well with most Hail teams. It also has access to Yawn and Roar to shuffle the opposing team around, accumulating damage from Hail and entry hazards. It can also use the gimmicky Hail (the move) in case your weather starter is down.
Heatran: Exceptionally useful as it absorbs all fire-type attacks aimed at your Pokémon, sets up Stealth Rock, Roars, Taunts, and a chunk of goodies. Better used as a bulky stallbreaker / Shuffler.
(Toxic) Spikes:
Froslass: No surprise here. Froslass can abuse Snow Cloak like crazy, using Brightpowder and sub at their better extent, while Spiking to rack up damage. Also, it is a spin blocker.
Forretress: Not only it can set-up both Spike and Toxic Spikes, it can also Spin entry hazards away! It also has access to a wide array of offensive moves, like Payback (for spin blockers), Earthquake (for steel-types that usually plague hail teams) and Gyro Ball for general madness.
Tentacruel: Like Forretress, it can set-up Toxic Spikes and use Rapid Spin to blow them away, as well a abusing a 100% accurate Blizzard.
Nidoqueen: Nidoqueen is both a great supporter with access to Stealth Rock and Toxic Spikes, but also an amazing attacker with Sheer Force boosted Earth Power and Blizzard.
Once you are done with the spiking core, you can add whatever you see fit as supporters (IMPORTANT: Wish is practically mandatory, as most Hail abusers do not have access to instant recovery - Jirachi, Togekiss, Latias and Vaporeon are all very effective at passing wishes (vaporeon has the added advantage of resisting fire)).
Spin blockers are very important (those are ghost-types btw) and you have to make sure you have at least one on your team, unless you want to be raped by well-organized stall teams. Those have to be bulky and act as effective pivots. The rotom forms were great but since they no longer exist, I would recommend Prankster Sableye, Eviolite Dusclops, Spiritomb, Jellicent or Chandelure. Chandelure is neat with Flash Fire, also.
Finally, try battling! Don't be afraid to try everything you can that looks nice, even things that are completely unrelated with Hail. Usually, Hail Teams have generic weaknesses to Fire types, Fighting types and Steel-types *cough*scizor*cough* so having enough checks to those is necessary. Don't be afraid to have Pokémon weak to Hail, that is why your Wisher is here (Having two wishers wouldn't be too much, actually).
Good Luck!
