You have F-zero already I see? Good choice.
No scratch that, excellent choice.
Anyways, my other favourite GC games were Wind Waker, Timesplitters 2 and Eternal Darkness.
BreakfastMan said:
killer7. It is crazy as all get out, but it is also one of the most unique games ever made. It is also one of the few games I would call a masterpiece. It is one of the best works of art that this medium has produced. killer7 is to games what Eraserhead is to film.
I'd recommend it, if only to try something completely unique. I didn't like it much myself, I never finished it. The art style and story were great, but I didn't like the gameplay.
But I'd certainly recommend it, because it's incredibly daring.