John GBA Lite is GBA emulator for android 2.2+. This app does not work without your own game files.

John GBA has good compatibility, smooth game play , and quality audio
Supports load/save states, cheats, external controllers, screenshots, speed increase, and dropbox.
This version has Ads. Ads appear as pop-ups while in menu and small banners at the top of the screen while in game play.
All and all a very nice emulator. If you don't like the ads either upgrade or, if you have a rooted device, check out Adfree.