The best GBA game I've seen is Yoshi's Island (Not for the SNES or DS, just GBA). It has great graphics music, and gameplay. It's also long and gets challenging as it goes on, unlike some others. It also has special twists hidden everywhere, instead of just running though the level, like minigame shacks. There's a ROM out there somewhere, try it :)
Project64
If I were you, I'd also get Mupen64 (if you like N64 emus). Mupen64 can speed up gameplay, slow it down, record it, and use button turbo. I like it; I recommend you try it and see for yourself. The only downside is that it doesn't allow cheat codes.
EDIT: I legally own a Gameboy Advance AND the YI cartridge. I also own my own N64 and the SM64 game itself. This is legal (for me anyway)
