Game: Tentacle Wars

Like tower defense, fast strategy games (I don't know if this is actually a genre, but if it isn't I'm coining it now) are a relatively young genre that have gained momentum on mobile platforms.  Their design lends themselves to mobile play.  The fast pace and simple control scheme makes fast strategy perfect for the touch screen and gaming on the go.  It's one of the few genres that feels like it belongs on an iPhone.  Tentacle Wars is one of the finer examples of this.  No clumsy virtual d-pads or gross approximations PC/Console control schemes, just a game the feels at home in your pocket.