Castlevania Circle of the Moon. I know the graphics are dark, but I still loved the game. My first GBA game reserved. When I worked at EB/GS I actually talked a customer out trading it in.
Otherwise, Advance Wars 1+2
Metroid 0 and Fusion
Hell even Namco Musem, worth it's weight in gold.
Super Mario Kart:Super Circuit
FF4 Advance, the first FF game I played start to finish. Holds a special place in my heart.
My Top 10 1.LoZ:LttP,2.SimCity(SNES),3.SMB3,4.FF4,5.SH,6.HL2,7.Portal,8.RE4,9.SMG,10.YI