i have a 1gb transcend sd card i got from newegg that works, i think it is an 80x as far as speed goes. i don't know very much about the compatability of sd cards and the gp2x are. i do know that some sd card makers have switched to the origonal version of sd cause they have found it to be faster. the new version of sd works on the same stuff but is different somehow, not sure how. it would be interesting to see if the compatability changed depending on what type of technology the sd card was based on.