Good news, Madfinger changed the price of their Dead Trigger FPS zombie shooter game from 99 cents to free! It's incredibly well made and lets you kill endless amounts of zombies.. Definitely check it out if you like shooters and/or zombies. Grab it in the Google Play Store.
Extensive 15 minute video review:
Dead Trigger Android Game (Video Review)
http://www.youtube.com/watch?v=RZ9HpmpLFR8