Mario is 100% correct - I can't believe you don't have Sunshine, Jungle Beat and Pikmin 2. Those are three of my top 10 GameCube games - it would be a crime not to own them. You can get them all cheap too. I honestly can't understand all the hate that Sunshine got - the controls were tight, the gameplay was great and FLUDD is seriously underrated. Pikmin/2 are absolutely brilliant - it's the best new IP of last generation. And Jungle Beat is pure bliss.. Many reviews say it's short, but I don't think the reviewers got past the first boss. To actually finish the game, you need to put in a few more hours. Then after that, when you're a pro, stringing together combos and finding the best way through each level is a joy.
Hmm. Well, I'd add in Soul Calibur II, Star Wars Rogue Squadron II: Rogue Leader, Burnout 2, Mario Kart: Double Dash, and Tales of Symphonia to the list. Even if you're not a big fan of RPGs, Tales is incredible, since it's very unorthodox - the battle system is in realtime. If you like wrestling games Day of Reckoning/2 are fun.
The only three games I'd give a pure 10 for this generation are F-Zero GX, SSBM and Pikmin 2. The second tier is Super Mario Sunshine and Eternal Darkness. Then after that you have the Metroid Primes, Wind Waker, Resident Evil 4 and Jungle Beat.