There are adapters, >>1. You can buy one in-store for a PS2-Xbox adapter, but as for gamecube, you might need to look online (they might be instore, though).

I agree. PS2/PS1 Analog controllers are the best. I also enjoy the Gamecube controller for casual playing, which is what I do on my gamecube - lately, though, I dislike the SNES controller. And Dreamcast isn't as bad as everyone makes it out to be.