My Circuit City just got in the latest Gamecube demo (#25, I believe) and it's got Donkey Kong Jungle Beat as a playable demo! It's pretty sweet. It took me a bit to get used to it, but before long I was banging the bongos like a maniac, probably freaking out some customers in the process. Obviously, you'll only be able to find it at kiosks that have the bongo drums already attached.
From what I can remember, it also has demos of RE4, Metroid Prime 2, Mario Tennis, Virtua Quest, and Star Fox Assault.