Heres a few that have be rolling around in my head.
Infection: All Poison effects are treated as badly poisoned while the pokemon with this ability is in battle
Desperation: Ups the Attack of the pokemon by 50% while its HP is below 33%. This attack boost disappears when the pokemon HP returns to a value above 33% and the effect cannot be Baton Pass'ed
Shifting Sands: Ups the Speed of the pokemon by 50% while in a Sandstorm. This Speed Boost doesn't apply on the turn it becomes Sandstorm.
Overcharge: Damaging Electric attacks with effects have their chance of the effect happening doubled, but the pokemon with this ability recieves 100% more damage from Electric attacks.
Zen: This pokemon ignores the effects of the following attacks on it: Taunt, Torment, Spite and Roar.
Calculating: All damaging moves with a base power of 60 of less ignore the effects of any move, ability or item that would negate, redirect or lessen the damage inflicted and the effects of defense/special defense stat changes