Paper Mario 2, The Thousand Year Door. I Borrowed it off a friend and am looking deperatly to find a cheap copy, but they're all about £20...
Starfox Adventures (I know this got some crap reviews, but its got a lovely environment, just a shame about the prince guy and the combat...)
Eternal Darkness: Great at night, with a buddy over, in the dark. Check the Bathtub...
Animal Crossing: Get your family to join in, and you have a hell of a game. Racing to pay off your mortage, racing to get items from nooks... Personally I didnt race to pay off my mortage, and just payed off a feww thousand every day.
Wind Waker and Twilight Princess: Well duh. They're Zelda Games.
Timesplitters 2: a million times better then Halo 3. Half as good as Goldeneye.
Super Smash Bros. Melee: possibly the best Multiplayer EVER.
F-Zero GC: I preferred it to Mark Kart: Double dash, which is saying something
Enough? want more?