Final Fantasy Tactics Advance -GBA-Turn-Based RPG-one of the best GBA games EVER Summon Night Swordcraft Sory 1 and 2 GBA-Quite fun- cool 2D battle system Legend of Zelda: The Minish Cap GBA- I love Zelda games, this has good graphics Tales of Phantasia GBA-Good if you like Tales games
try the Hajime no Ippo game for the GBA. it's less similar to the previous HnI games, and a bit more like Punch Out.
Earthbound, DBZ Supersonic Warriors, Dragon Quest Caravan Hearts, Dragon Quest 1,2,3 (also for the SNES) Basically every Pokemon game you can get yours hands on for the GBA/GBC, Dragon Warrior Monsters 1/2, Metabots Metabee Version or Rokusho Version Sorry about the long list, but I have all of these and they are so fun!
Pokemans for GB/C/GBA Legend of Zeldas for GB/C/GBA Mother 3 (with fan translation if needed) GBA Yu-Gi-Oh Dark Duel Stories GBC Lufia GBC
Deffinatly get either Pokemon Gold or Silver, it's time to get back to being used to grabbing the metro to Saffron, with the impending release.
boktai fun if played in real gameboy advance and sucks if played in emulator(like VBA).... anyway,be sure to try it!!