castaway with- Stunt Car Racer, Sentinel, Dungeon Master, Bubble Bobble, Sentinel IK +, and Buggy Boy
gp2600 with pitfall and beam rider (and why not put in ET to witness what has been called the worst game of all time??!! see just why atari buried millions of carts in the desert!! lol)
gpvgb with tetris DX, super mario bros dx, ghosts n goblins, game and watch gallery 2 (all fun for wasting a few minutes with, but the emu doesn't seem to support saves so I wouldn't bother with zelda, ffa etc until it works!)
speccyal k with matchday 1 and 2, manic miner, jet set willy, knight lore, atic atac, head over heels (although it might also work with castaway but I haven't checked..), target renegade, chuckie egg, finders keepers, jack the nipper 2, jet pac, scuba dive, splat, turbo esprit, thrust, cyclone, tll, wheelie, zub, bruce lee (doesn't seem to work with frodo :-( )
frodo 64 with way of the exploding fist, dropzone, last ninja, paradriod, park patrol, rambo, beach head 1 and 2, impossible mission, kane,
sms32 with action fighter, choplifter, ultima 4, sonic 1 and 2, world class leaderboard, baku baku animal, sonic spinball
gpengine with adventure island, bomberman 94, columns, devil crush, dragon spirit, galaga 88, parodius, shinobi, volified
xcade with donkey kong, donkey kong jr, pheonix and space invaders
fmsx with goonies, metal gear 1 and 2, ping pong, hypersports, yie ar kung fu and penguin adventure
scumm with monkey island 1 or 2...
hope that helps. there's a few for you to start off with, however it all depends on what sort of games you like!
moora101