Froslass, who has moves like Thunder Wave and Spikes to support its team. Froslass discourages enemy leads from taking it down with Destiny Bond, and has powerful Special moves in Shadow Ball, Ice Beam and Thunderbolt to back it up. Froslass can also Trick a Choice Scarf onto its opponent.
Uxie, with moves like Stealth Rock, Reflect, Light Screen, Thunder Wave, U-turn and even Memento to help its team win should not be ignored. It also has a fair Speed and very nice bulk.
Ambipom, whose Technician Fake Out devastates frailer leads. Ambipom is a reliable weather starter, as well as carrying U-turn, Low Kick, Shadow Claw and Return. Ambipom can also use Taunt to screw over slower leads.
Moltres, who often wields a Choice Scarf to outspeed and destroy leads before they can blink. Moltres carries a ridiculously strong Overheat, as well as Will-o-Wisp for team support and the ever useful U-turn.
Alakazam, with a very strong Psychic, as well as Reflect, Light Screen, Encore and Trick can screw over your opponent's lead, as well as helping out your team.
Electrode, the infamous Rain Dance lead. Electrode is rarely seen without Thunder/Taunt/Rain Dance/Explosion, which allows it to stop the opponent from supporting its team, setting up Rain Dance for your team, and then finish with Explosion.
Omastar, who can set up all three of Stealth Rock, Toxic Spikes and Spikes, and use Surf to discourage Pokemon like Donphan coming in to Rapid Spin them away.
Hippopotas, the only Pokemon capable of summoning infinite Sandstorm in UU. Hippopotas also carries Stealth Rock, Yawn and Roar to support your team and screw over your opponent's.
Rhyperior, who has a massive Attack stat and Stealth Rock to boot. Rhyperior can dent an opponent's team with Stone Edge and Megahorn, or go the support route.
Cloyster, one of the only Pokemon in UU capable of setting up Spikes and Toxic Spikes. Cloyster also has Ice Shard for a good priority move, Explosion and Rapid Spin.
Arcanine, who has a great STAB in Flare Blitz, as well as Extremespeed for finishing off weakened enemy leads. Arcanine also has Morning Sun to heal itself in a pinch. Arcanine also has moves like Thunder Fang and Hidden Power for coverage.
Venusaur, when equipped with a Choice Scarf, is a great hybrid lead because of Sleep Powder, which incapacitates your opponent's Pokemon (assuming they aren't using Lum Berry) and powerful STABs in Power Whip and Sludge Bomb to wreck the opposition.
Hariyama, with a powerful Close Combat and priority in Fake Out and Bullet Punch is an offensive lead to watch out for. Hariyama also has Guts to discourage status from being used against it, though Sleep can put it out, which is why some Hariyama leads use Sleep Talk.
Kabutops, boasting standard hybrid lead moves like Stealth Rock and Rapid Spin, whilst still being able to hit hard with Stone Edge and finish off a lead with Aqua Jet means that Kabutops can fit well on just about every team.