Mario 128, Pikmin 2, and Animal Crossing 2 have all been confirmed by Shigeru Miyamoto in interviews and such (check IGN for proof). Factor 5 is working on a game (not Thornado, that is cancelled), and Silicon Knights is actually working on more than one game, but the only one we know of is Too Human.
Nintendo's 6 developers and their 2003 games (off the top of my head):
NST - 1080: Avalanche
Silicon Knights - Too Human, unannounced game
Retro Studios - Metroid 6 (tentative title of course, also probably not till 2004)
Intelligent Systems - no known GCN games, GIVE US CUBE WARS!!!!!!
HAL Labs - no known GCN, hopefully Smash bros online or 3
EAD - Zelda, Donkey Kong Racing, Mario Kart, Pikmin 2, Animal Crossing 2, Mario 128
Also one of the above is working on a pokemon game, if its Stadium then it's HAL but if not who knows, probably EAD
2nd party games:
NDCube - Tube Slider
3rd party Nintendo games
Treasure - Wario World
Amusement Vision - F-Zero
Namco - Star Fox Armada
3rd party exclusive
Capcom - PN03, Dead Phoenix, Killer 7, Viewtiful Joe (RE4 not until 2004)
SEGA - Sonic Adventure DX
Ok i gotta go know but those are all from the top of my head there are more.
The biggest games are without a doubt Zelda, F-Zero, Too Human, Animal Crossing 2, Star Fox Armada, Mario Kart....of course many more will be released. Oh and am I the only one tired of Sonic Team's crap? We get pretty much exclusive Sonic Team stuff and they give us old junk. What's up with that. I want a new sonic game, with only high speed classic action, no digging or shooting junk....