Third party support for the GC is dead, but we've still got another round of games left from Nintendo. The first party is honestly doing a pretty decent job of providing titles on its own for this year, all things considered. Maybe some will be pushed to 2006, but I think we'll have Fire Emblem, Kirby, Geist, Advance Wars and Zelda this year.
As Ian said, 2006 will probably be N64-bad. If it ISN'T horribly dry, it will be because
a) Nintendo Revolution is released before the end of the year or
b) Nintendo makes more GC games at the cost of a better Revolution line-up.
(b) would just be foolish, but (a) is a possibility. I have no idea how well a July console launch would work, but September was OK for GC in Japan.
MS is really in a good position to get GC-but-not-Xbox owners for the next generation. MS is cutting its own Xbox's life short, and PS2 fans can probably wait for the PS3, but with the right software near launch Xbox 360 could punch Nintendo in the stomach. If the first party support in 2006 is as horrible as I expect, I know I'll need another console unless the DS is brimming with good software.