gpSP is a well known emulator for Gameboy Advance, available for a bunch of systems and now ported to Caanoo!

Plenty of GBA homebrew games can be downloaded legally and free of charge here at PDRoms from: //files/gameboyadvance/

http://dl.openhandhelds.org/cgi-bin/caanoo.cgi?0,0,0,0,71,529