Love lots of the suggestions!
What about these?
Well Rested: If this pokemon is afflicted with the sleep condition, it restores 1/4 of its HP every turn that it is asleep.
Dazzle (for Steel-types, or pokemon with gemstones/crystals like Sableye): In sunlight, the opponent's accuracy is lowered one stage.
Flytrap (for Victreebel, Carnivine, etc.): Bug-types moves do 25% less damage.
Closed Mind: Psychic moves do 25% less damage.
Intangibility (for ghosts): Walls and screens (Barrier, Light Screen, etc.) cannot be used while this pokemon is on the field. (based on ghosts being able to walk through walls and objects)
Nasty Streak (for rodents like Raticate, or pokemon like Gengar): Dark-type moves do 25% more damage.
Airborne (for Flying-types): Flying-type moves do 25% less damage.
Cautious: If this pokemon is PAR, BRN or FRZ, its speed lowers 2 stages, and its defence raises 2 stages.
Muscle Soothe(for Fighting types): If hit with an Ice-type move, the pokemon's attack increases by 2 stages.
Corrosion: Poison-type moves work on Steel-types (x1 damage)