iMech, Minigore, Inkvaders, Doodle Jump, Battle Bears, CatchCows, Cowabunga, Zentomino, My Brute, Alive 4 ever, Stacked, Run! (amazingly awesome game, must have) and Baseball Slugger.
I think Beseigement and Airport Mania are two of the more under-the-radar $.99ers that I've played, especially if tower defense and time management (respectively) are your genres of choice.
