SSBM of course.
Mario kart Double Dash is my favorite in the series, and has the best rainbow road.
Luigi's mansion was great, regardless of what anyone else says. Who honestly went into that game thinking it was gonna be a platformer?
Super Mario Sunshine was good as well, but not without it's problems. Swimming was clunky, but wasn't used all that often. The hover nozzle felt clunky as well, and this I feel was the most irritating problem. There were some camera issues. God damn were some of the stages hard.
Pikmin and Pikmin 2 are pure gold.
Metroid Prime 1 and 2 are great as well, but it could be difficult to read the map at times.
Wind Waker and Twilight Princess are excellent, as is usual for the Zelda series. Four Swords Adventure is also worth taking a look at. Even single player, This was an excellent game, but many complain about the multiplayer requiring a lot of extra stuff to play (a GBA and a cable for each player). If you don't have all that extra stuff, the single player mode is still worth it.
Sonic Adventure was absolute proof that 3d was the best thing to ever happen to sonic. I'd say Sonic Adventure 2 was as well. The Sonic/Shadow levels were pretty much what you'd expect. The Tails/Robotnic (oh yeah, I called him Robotnic) were slower, but you are riding a freaking robot and blowing up everything that moves or you just feel like blowing up. The Knuckles/Rouge levels are difficult to love, but become much better once you learn to navigate each level. The rap "music" on the Knuckles stages is just gadawful, however. Sonic Heroes was good, but the dialogue felt a little too childish mot of the time. There were a bunch of glitches regarding switching attack modes and the camera, but the game is far from unplayable (usually anyways).
Paper Mario 2 The Thousand Year Door was absolutely awesome. The humor is a bit outdated, but it blends ARPG and TBRPG elements incredibly well, and provides significantly more depth and challenge than the previous game.
James Bond Nightfire, as well as Agent Under Fire are pretty typical Bond games. That is to say, pretty good. Everything or Nothing is unique in that it is in 3rd person perspective, but that didn't really mesh all that well with me.
Star Wars Rogue Leader is pretty much exactly what it sounds like. The Clone Wars shakes things up a lot, with most of the combat taking place on the ground. The fighter tank, walker, and gunship levels are great, but the jedi levels feel unpolished. it has a good multiplayer mode as well.
Resident Evil. Just, Resident Evil.