Ive always been a gameboy fan (not that ds crap).
Final Fantasy's Tactics Advance and Dawn of Souls are both good.
Mega Man Zero games are also surprisingly fun and adicting.
Metroid Fusion and Zero Mission (zero mission is better)
Castlevania: Aria of Sorrow is great, but all the other castlevanias on gba really suck
(I have a lot of gba roms
)