Well,I recomend Aurora Feint 3 which is essentially Puzzle Quest (Bejeweled welded to a basic RPG). Slide gems and match three to gain energy or smack your foe during battles. The horizontal-only sliding combined with accelerometer-based gravity-shifting in the well means you have to think fast in this game, which is well-suited to the iPad.
Picked up Alien Breed last weeked for 0.69p hoping to relive the Amiga days but unfortunately the game doesn't transfer well to being played on an iPad.
Others I'm enjoying are Bowling Wizards and Catapult King.
Catapult King is a great one to sit down and play with the kids