There she be, folks -- Fieldrunners HD. It's tower defense done like never before, with excellent graphics and sounds. It's got more than 400 levels and four battlefields, seven towers and three difficulty levels, plus two additional modes once you beat the Classic game.
Fieldrunners HD is a pretty big download at 36MB, and it's available on Android smartphones (not tablets yet) running Android 2.2 and up. Download it from the Amazon Appstore for free today at the link below.
Download: Fieldrunners HD