I would like to see Picodrive for the N9, it's a SEGA Mega Drive emulator with support for the Mega CD.

PCSX ReARMed would be quite nice too. Would be really nice if I could play Chrono Cross on the phone

gpfce is quite fast NES emulator which also can play .nsf sound files.

And the most important one is ScummVM, which is fortunately already on the list and planned to be ported to the N9