1. Garchomp - I'd rather not rehash all of the arguments that "possibly" make it Uber, but we're all completely aware of its sweeping capabilities. Reason #1 for using Ice attacks.
3. Gengar - Its use has gone up quite a bit in the last few months, and with good reason. #1 reason for using Dark attacks. Damn that 130 SpA and 110 Spe... thanks for making me have to carry Pursuit for you!
4. Gyarados - Reason #1 for using an Electric attack.
5. Tyranitar - Reason #2 that I have to pack a physical Fighting attack on my team. (#1 was Blissey, remember.)
6. Lucario - Several viable sets for it to run, and Extremespeed to boot.
7. Heatran - Reason #1 for carrying a Ground attack. 130 SpA WITH 91/106/106 defenses? Son of a BITCH!
8. Metagross - I run this on my own team. 135 Atk hurts and a STABed 100 BP move that can RAISE its Atk is always a mess to deal with.
9. Salamence - Reason #2 for using Ice attacks. 135 Atk, 100 Spe, Dragon Dance; need I mention the 110 SpA, as well?
11. Infernape - I don't think I can count the number of RMT threads I've seen where teams are noted as being MixApe weak. Definitely an effective wall breaker. (Gyarados, Starmie, where are you?!)
13. Weavile - Reason #3 for packing a Fighting attack. 125 Spe and 120 Atk to boot. Did I mention Ice Shard and Pursuit?
18. Starmie - I would think that having Gyarados and Gengar covered reduces the need to pay special attention to Starmie, but Infernape users have to worry about it, and it can Recover much of the damage it takes switching in.
19. Breloom - Reason #2 for using Flying attacks. The #1 reason is next, but Breloom seems to be used more for its Sporing and SubPunching/Seeding prowess.
20. Heracross - Reason #1 for using Flying attacks. Megahorn and Close Combat are two very potent STABs off of 125 Atk. Stone Edge and Pursuit / Night Slash on top of that? Check please.
21. Togekiss - Speaking of Flying attacks, here's the #1 user of them! I'm personally most worried about its ParaFlinching capabilities, though. 30% chance of attacking? Give me a break!
24. Azelf - 125 SpA, 115 Spe, 125 Atk (for U-turn and Explosion), Nasty Plot. There's a reason I use Azelf on my team. Reason #1 for using Spiritomb. :naughty:
26. Snorlax - My God, what a tank--and a self-destructing one, too...
30. Porygon-Z - If it weren't for the infamous 'Nasty Plot Life Orb Adaptability Hyper Beam,' I wouldn't worry as much, but 135 SpA and Nasty Plot can still be a mess to deal with.
32. Magnezone - BoltBeam resist, Skarm trapper. Reason #2 to use Ground attacks.
33. Yanmega - A fast Hypnosis that only gets faster; yay. Bug Buzz and Air Slash from 116 SpA is nothing to scoff at, either. Probably the #1 reason to use Stealth Rock, if not #2 (Charizard).
35. Mamoswine - 'You're Mamo weak' seems to be a popular RMT meme, but being immune to Sandstorm and Hail (complete with Snow Cloak) and posting a nice 130 Atk, Mamoswine can take advantage of the STABed Earthquake / Ice Fang/Shard combination offered to it. The 110 HP is nice, as well (because 80/60 sure won't cut it), and the 80 Spe is icing on the cake. (Fuck you, Heatran!)
37. Machamp - 130 Atk and Guts or No Guard Dynamicpunch. Certainly anything with 130 Atk must be looked out for, anyway, but an attack with a 100% confusion rate (Ghosts notwithstanding) may give several Machamp counters second thoughts about switching in. Possibly the #2 (if not #1) reason for ever using Slowbro.
40. Jolteon - The second fastest Passer in the game and 110 SpA to boot. Jolteon may be the #2 reason for carrying a PHazer. (Ninjask is #1.)
43. Dugtrio - Traps grounded opponents like a pro. Like the original threat list states, it "makes you think twice about building a team loaded with Pokémon Dugtrio can kill off easily."
45. Dragonite - A little more defensive than the other OU dragons and holds a candle over them with Dragon Dance and Outrage. DD+Outrage is the ONLY reason I include Dragonite here as it is as similarly dealt with as Salamence.
51. Alakazam - 135 SpA and 120 Spe; no non-Uber can boast that combination of [Sp]Atk and Spe. Though it might be just another Special Psychic Pokemon, it can also carry Trick to mess up common walls by giving them Choice Specs.
52. Aerodactyl - 130 Spe makes it a prime candidate for Choice Band and Life Orb. That 105 Atk isn't bad, either.
53. Gallade - 125 Atk that can be boosted through Swords Dance, 115 SpD, and Hypnosis/Thunder Wave/Will-O-Wisp to cripple many of its counters.
55. Rhyperior - I'm sorry, but 115 HP, 130 Def, and 140 Atk can still cause problems, especially in sandstorms. Further justification for Grass Knot (also for Swampert among other things) and Water attacks--and possibly weather changers (which you should also consider for Abomasnow).