Pogoshell is the most innovating program made for your GBA/Flash card. It's like an operating system that allows you to manage roms, savefiles, play music and view images with a simple graphical interface.
(http://www.geocities.jp/gbmogiki/pic/pogoshell2.gif)
http://gbatemp.net/pogofaq/index.html (http://gbatemp.net/pogofaq/index.html)
Well, a nice tool for the GBA :D You can play MODs, NSF, MIDI, WAV and other stuff..
And turn your Gameboy Advance (micro) into a portable MOD player ;D