General Rules
Species Clause - A player cannot have two Pokemon with the same National Pokédex number on a team.
Sleep Clause - You lose if, at the end of your turn, two of your opponent's Pokemon were put to sleep by a move you used but were not forced into, and neither have had their sleep removed since then.
Evasion Clause - A Pokemon may not have the moves Double Team or Minimize in its moveset.
OHKO Clause - A Pokemon may not have the moves Fissure, Guillotine, Horn Drill, or Sheer Cold in its moveset.
Ubers are banned from OU downwards.

Ubers
Code:
Mew
Mewtwo
OU
Code:
Alakazam
Chansey
Cloyster
Dragonite
Exeggutor
Gengar
Golem
Jynx
Lapras
Persian
Rhydon
Slowbro
Snorlax
Starmie
Tauros
Zapdos
UU
Code:
Aerodactyl
Arbok
Arcanine
Beedrill
Blastoise
Butterfree
Charizard
Dewgong
Ditto
Electabuzz
Electrode
Farfetch'd
Fearow
Flareon
Golbat
Golduck
Hitmonchan
Hitmonlee
Kabutops
Kingler
Lickitung
Machamp
Magmar
Magneton
Marowak
Muk
Ninetales
Omastar
Onix
Parasect
Pidgeot
Pinsir
Poliwrath
Porygon
Primeape
Rapidash
Raticate
Sandslash
Scyther
Seadra
Seaking
Tangela
Vaporeon
Venomoth
Vileplume
Weezing
Wigglytuff