The Mushroom Kingdom is a fan site that talks all about Mario, his history and that stable of characters. I love the encyclopdedic reference for all the characters, including all the minor bad guys, with images.
In related news, the Game Boy Advance is out in Japan. Kind of a sideways gameboy, but it can play games on par with the SNES (circa 1992 or so), instead of just the old NES (circa 1985 or so). When it comes out here in a few months, it's supposed to be retailing for $99! That's going to be a really interesting system. I'm almost sorry I got a Game Boy Color for Christmas, it's so outclassed by this one-- plus it has four player linking, including a feature with some cartridges that only one of the units has to have the game, the rest get what they need over the link. Neat.