Since the Wii is completely backwards-compatable with GCN, I figured we could post some great GCN games here.

-Super Mario Sunshine
-Luigi's Mansion
-Super Smash Bros. Melee
-Metroid Prime
-Metroid Prime 2 : Echoes
-Kirby's Air Ride
-Mario Kart Double Dash
-Pikmin
-Pikmin 2
-F-Zero GX
-Eternal Darkness : Sanity's Requiem
-Metal Gear Solid : The Twin Snakes
-Tales of Symphonia
-Donkey Kong Jungle Beat
-Resident Evil (REmake)
-Resident Evil Zero
-Resident Evil 4
-Baten Kaitos
-Baten Kaitos Origins
-Odama
-Killer 7
-Def Jam : Fight for New York
-SSX Tricky
-SSX 3
-SSX On Tour
-WWE : Day of Reckoning
-WWE : Day of Reckoning 2

* plus I know there's plenty more...