K-teto has updated his port of Gnuboy for the GP2x again. Release notes:

I don’t have a webpage right now, so… tracking the changes is difficult, i know. But when gnuboy2x 0.3b was just added to the news here, 0.4b was out already. And here you have it, with better sound, faster screen code and many bugfixes. And more important, HARDWARE SCALING for full screen gameboy madness, yeah, you like it b*tch.