I played both BL and UU a lot, before. I'm currently on an OU roll, so my information may be outdated. Also, like Shiny Oddish, UU play is too sparse to consider anything too common. However, I have an interest in using UU pokes in OU as well. Here's my thoughts on UU pokes:
Pelipper has had stellar performances on my team. Ice Beam, HP Electic, Surf and Roost have taken down many a foe in OU, and I've done well in UU with it. It's Water/Flying typing seems great in UU, but beware of Rotom and Manethric, and of course Lanturn. Also, I am considering an Agiliper that could possibly outspeed OU AND UU and blast away, with possibly HP Ground to wallop the Electric switchins.
Cacturne did very well for me, and I actually thought it was BL. Sash-couter, Sash-SD, Sash, Sucker Punch, and Seed Bomb. I usually won the prediction wars that followed. It could wreak havoc in UU.
Hitmontop, while a controversial pokemon, I think is UU. Both defensive Bulk Up Intmidate sets, Technician offensive annoyer sets, Banders, all are there to wreak havoc on the unprepared team. However, one can usually guess what it is as soon as it comes out (Intimidate or no Intimidate?).
Altaria, the Dragon of UU. Like cousin Salamence in Standard, this cotton-pluff cutesy Dragon will keep you guessing what it's set is until it actually makes a move. Switch in Hypno? Say hello to a DD in the face and then a nice Dragon Claw in the face. Switch in Sandslash and say hello to SpecsMeteor. Annoying, but once you know it's set it's pretty predictable.
Persian, the faster and skinnier cat. As a lead, it can be either two things: Hypnoplot, or Fake Out Technician versions. Switch in a Lum Berry Drifblim and make it pay for using sleep moves :). It can be pretty annoying, but it goes out quick and does not do to much damage.
Also, an intersting option is Switcheroo.
Ninetails is as controversial as Hitmontop, but UU for now. Hypnoplot is the standard, though it has a variety of other options. Energy Ball, Fire Moves, etc. Standard fire type.
Purugly, the fatter cat of the two, though not that much slower (surprisingly). 112 outspeeds even Gengar in OU. It's more offensive physically, though it's 1 point behind in Sp.Attack and lacks Nasty Plot. It's only slightly more defensive. It's abilities aren't besting Technician and Limber, and it does not have Switcheroo. It still has Hypnosis, and it also has Sucker Punch. Useful for HP Fight Electrodes trying to nail you. Basically, it's a more effective physical attacker than Persian, and that's it. Still, useful.
Sandslash is, as Bologo noticed, Donphan Jr. It can set up the Rocks, Rapid Spin, and can Thief items. It also has SD for an offensive flavor. Too bad it lacks Ice Shard.
Blastoise is the Bulky Water of the joint. It spins, hazes, can Countercoat. It can Yawn, and Toxic (err...). It's favored more for physical tanking/walling.
Butterfree will pop up as a lead alot, usually Double-Stausing (Doublepowder: Sleep Powder, Stun Spore). It usually carries a sash. It can U-Turn and WW you away. It can Roost... but eh. Doublepowder is it's best use, but it can wreak havoc.
Nido-royale, the bulky and offensive versions of one pokemon. Queen usually carries out regular tanking duties (Toxic Spiking, etc.). King uses his offensive powers and two similar stats to blow your team away mixing, or staying on one path.
Kangaskhan can be a lot of things. Bulky or offensive. Subpuncher with Scrappy or tanker with Rest+Early Bird. It has even Outrage. It has Sucker Punch. It can Endure/Reversal w/ Scrappy. It can use Wish. It can Sing. But, it's the jack-of-all trades, master-of-none.
Chatot it an interesting special bird with Nasty Plot, Chatter, Encore, Hyper Voice, and Sing, U-Turn as other options. Hidden Power Fight as well. Rotom can easily come in on it, however.
Rotom was mentioned a lot before. This was mostly due to it's fantasticly innovative and refreshing typing. It can Trick, Burn, paralyze, or just plain attack. It's pretty fragile, but it's speed and sp.attack are good.
Grumpig, Psychic sp.defensive guy #1. He has good sp.defense, but unlike his partner in crime he is less wallish and more offensive. CM is his greatest asset. He has Thick Fat.
Hypno, Psychic sp.defensive guy #2. He has great sp.defense, but his offense is mediocre. Switcheroo/Trick, Hypnosis, Nasty Plot/Belly Drum Baton Pass... He can checkmate your team easily. He can't do much back, however.
Probopass, Mr.Potato of pokemon. He has both good defense and sp.defense, but most people prefer sp.defense. He has Magnet Pull. He has OK sp.attack to obliterate weaklings like Sharpedo. He is the member of the Rock/Steel club along with
Aggron, who most definetly has better defense than sp.defense, is another member of the rock/steel club. He has good attack as well. If you're physical and dont have a way of dealing with him, he can stall you forever.
Shuckle is another huge defenses guy, but he has abysmal HP. His support options are numerous (Encore, Knock Off, etc.) but he has NO offense and no recovery outside of rest. Still, he is good.
Swellow has that scary Facade/Guts/Burn Orb combo alomg with U-Turn and Brave Bird. Yeah.
Poliwrath is controversial, but UU for now. Belly Drum, Hypnosis, Focus Punch, Water Absorb, etc. are great. He can also Bulk Up for pain.
Politoed is the pampered version of Poliwrath, the prince rather than the pauper. As a special wall, he's OK. Hypnosis, Surf, Water Absorb, Seismic Toss, Ice Beam. He can Belly Drum up if you want to go for surprise.
Meganium is a mixed wall by stats, but a physical wall by preference. Leech Seed, Light Screen, and a lot more populate this grasser's movepool. Typical grass... Though he's pure grass, interesting.
Vileplume. I HATE A VILOPLUMESS! ESPECIALLY WHEN THEY HAVE SUBSTITUTE! This says a lot about the fear people have of Leech Seed Vileplume. Excelent defensive stats and subseed make it something to fear. Pretty good. SD Vileplumes and specs ones are seen as well.
Kingler, the crap. Crabhammer, X-Scizzor, etc. SD. Basically a physical water type powerhouse. It's 115 defense is nullufied by 55 HP and 50 Sp.Def, IMO. 75 speed is OK.
Sharpedo is another water-type powerhouse, but he's as fragile as cardboard. He has good movepool, sp.attack, attack, and speed. Watch out for this.
OK, I'll update the list as I go.