Okay, I once made a homebrew pixeleditor of the Sony PSP and an unfinished one for the Nintendo DS. Today I discovered this pixeleditor for the iPhone, called 32×32. It looks very interesting. It features only 32×32 pixels and grayscale 5-colors palette. The usability aspects of doing pixels on the go seem to be solved in an elegant way. Just see for yourself:
dude, please finish the ds one. i would pay good beans for it if it could export files. ;)