I'll give a few suggestions that haven't been made yet: Super Mario Sunshine, though I'd rent it first. Some people, like me, love it, but others were disappointed. There are also many other games that I like/have, but I dare not recommend them, since they are very genre particular.
Luigi's Mansion is a lot of fun, but take heed, it is rather short. I'd recommend it, though, especially if you can get it for cheap. Super Smash Brothers Melee is a must-have, no joke. Some good games that are coming out include F-Zero GX, Mario Kart: Double Dash, Pikmin 2 (methinks it's coming out fairly soon), Mario Golf (has anyone seen the commercial for this? I thought it was pretty of funny), and many others, including games from the Capcom 5 and other Nintendo/Nintendo franchise games (Sega, for example, is making F-Zero, a Nintendo franchise). I'm also getting Kirby's Air Ride, another racing game, but I'm not so sure I should recommend it, since it is "TEH KIDDIE!!!11!!!" Looks fun to me, though, and you may want to do some research on it.