Super Smash Bros. Melee/ Excellent choise, should be in every Cube owners game collection
Metroid Prime/Also must buy
Resident Evil/If you like survival horror, must buy, but you should buy other one first(or rent) To make sure you like it.
Resident Evil Zero/look previous
Super Mario Sunshine/I like it, but some people dont seem to like the water gun feature, Its one of them Love or hate games, if its possible, give it a rent first.
Animal Crossing (your wife would like)/I like it, ten times funner than Sims, nuff said

StarFox Adventures/ Excellent graphics, but some people were little disappointed(Id give it 8/10)
WWE Wrestlmania X8/I dont think you should buy it, because WWE Wrestlemania XIX is coming in this month(or next, cant remember, probably next) Which seems much better.
The Legend Of Zelda: The Wind Waker/Must buy, my Favorite on GC.
Eternal Darkness/Also must buy, one of the most underrated games ever, and one of the best this generation has to offer.
Ikaruga/Havent played, but heard good things about it.
Luigis Mansion/Not too long game, you can go through it in a rent, fun though.
Skies of Arcadia Legends/If you like RPGs, you should get it.
I also recommend Pikmin, Star Wars: Rogue Leader(Notice, seguel to both these games are coming this year, and both seem to be better than theyre first parts. Also Mario Golf(out now in US) And MArio Kart seem like must buys. And MGS: Twin Snakes, Pokemon Colosseum(If you are into pokemon) is coming this year, and you should not forget F-Zero and Viewtiful Joe.
Yep yep, holiday games are sure looking good for the ´Cube.