Tower defense. Tower defense. Tower defense. There's definitely no shortage of TD-style games for Android. Don't' get me wrong - TD games are great. There are just a ton of them. Game development firm 11 Bit Studios must've realized that, too, so they went to the lab and carved away at their popular tower offense title Anomaly Warzone Earth and brought it to Android.
Update: For those who don't have access to the Amazon Appstore (or even those who do and prefer not to use it), this game just landed in the Android Market. Go blow some stuff up.