43 games. . . dang.
If you check out the Gamecube discussion thread, there's a thread near the top about "What game should I get?" Check that out, if you want.
But some personal suggestions are Metroid Prime, F-Zero GX, Kirby Air Ride, Super Mario Sunshine, Super Smash Brothers Melee (definitely. No way you should not get this game), and Luigi's Mansion, among many more. . . oh, and Super Monkey Ball is really cool.
Also, if you don't have a Gameboy Advance, check out the Gameboy Player. Got some good games. . . Mario and Luigi Supersaga is an awesome RPG, and other games like Metroid Fusion and Fire Emblem are available as well. As for RPGs for Gamecube. . . Skies of Arcadia is out, and Crystal Chronicles is out relatively soon, I think. I'm not sure, though, because I'm not a big RPG fan (Superstar Saga was my first one all the way through).
Good luck!