Nintendo FINALLY put up demos of a few WiiWare games on Monday. If you need a break from Mario, you can check out demos for FFCC: My Life as a Dark Lord (pretty fun), Beat.Trip Beat (fun but difficult), Pokemon Rumble (extremely repetitive), NyxQuest, and World of Goo. I haven't tried those last two yet.
Also, since no one took me up on my offer to sell my copy of Doc Louis' Punch-Out, I played that as well. Having yet to play the full game, this is basically a demo for me, and I really like the graphics and voice acting, but man do you have to be perfect to win. Once I figured out his pattern, I basically had to do it without getting hit since the time limit is extremely unforgiving. It's neat, but I'm not going to blow $50 on the full game. Maybe when it gets much cheaper.