^
While I do agree that the DS and PSP are a lot better than the GBA, the GBA still has a very nice list of games
As stated before the Fire Emblem series is a rather fun Tactical RPG
Final Fantasy Tactics Advance seems to be fun, I've never played, but one of my friends say that it no where near the greatness of the original...I've also never played that.
All of the original Final Fantasy games (besides the real 3, that ones on the DS) have been remade for the GBA
Golden Sun is also another fun RPG that you may be interested in
I'm a fan of the Zelda games, but never listen to me about Zelda, as I'm always biased about it
The Super Mario games and the Sonic games are also pretty fun, just good old classic Super Mario, and good old classic Sonic the Hedgehog.
And of course theres Pokemon, thats always good.
OH, and just in case you didn't know, the DS plays GBA games as well, unfortunately it does not play original Game Boy or Game Boy Color games, which is why it's a good idea to keep you're GBA.