K-teto has ported the open source Gameboy/Color emulator Gnuboy to the GP2x! It seems to emulate most games at full speed. More information in spanish language can be found at the original release thread. There doesn’t seem to be a file selector yet, so the ROM needs to be named rom.gbc. Update: There is NO sound and NO possibilty to control anything yet.

http://www.gp32spain.com/foros/showpost.php?p=303128&postcount=15