The Gamecube has a few amazing games that are exclusive to it, but with the PS2 having the much better controller, the multiconsole titles that were on both consoles were always purchased for the PS2.
My entire Gamecube collection. It was larger, but I sold off a lot of the multiconsole titles if I've had them on other consoles and a lot of Mario games/Smash Bros Melee to a friend.
Resident Evil
Resident Evil 2(port)
Resident Evil Zero
Phantasy Star Online Episodes 1 and 2
Phantasy Star Online Episode 3
Legend of Zelda Collector's Edition
Legend of Zelda Wind Waker(in my opinion one of two good 3d Zelda games)
Skies of Arcadia
Mobile Suit Gundam Fighters Locus/Ace Pilot
Tales of Symphonia
Metroid Prime
Fire Emblem Path of Radiance
I might pick up Wave Race again, but not sure why I sold it. Whether it just wasn't as good as Wave Race 64 or if I just didn't like it at all. I know I didn't like F Zero GX is the reason I sold that one, although I love the N64 game.