Well, a list of upcoming first and second party Gamecube and Game Boy Advance title have been released by igncube.com, who in turn apparently got the information from a popular multimedia magazine in Japan. The list goes as follows:
Pokemon Channel With Pikachu (GCN, 7/18)
Pokemon Coliseum (GCN, Fall)
Mario Golf (GCN, September)
Mario Kart (GCN, this year)
Mario Party 5 (GCN, this year)
Pikmin 2 (GCN, this year)
Wario World GC (GCN, this year)
Custom Robo GC (GCN, this year)
Star Fox (GCN, release TBA)
Super Mario Advance 4 (GBA, 7/18)
Pokemon Pinball Ruby & Saphire (GBA, Summer)
Legend of Starfee 2 (GBA, September)
Mario & Luigi RPG (GBA, this year)
Note that the Star Fox title listed here is NOT Star Fox Armada from Namco; thus, there are TWO new Star Fox titles coming to the Gamecube, the latter of which is presumably from, dare I say it, Nintendo EAD. Pokemon Coliseum is most likely a new Pokemon Stadium with two-on-two support, all of the new Pokemon, moves, items, personalities, and traits, and possibly LAN/online capabilities. A new Mario Party is always fun news, and I'm THRILLED to see the inclusion of a new Mario RPG game, of which Luigi's name is in the title (however tentative that name may be). All in all a very exciting list, and it doesn't even detail all of the other great Nintendo-only releases like Rebel Strike, The Twin Snakes, and Resident Evil 4.
I just hope Pilotwings GC pops up at E3 in addition to all of this.