Experience Music Project
EMP is a museum devoted to music and memorabilia. Their online presence is a great site, the kind you can get lost in for awhile. Among other things, there are exhaustive articles devoted to artists such as Jimi Hendrix (EMP's patron saint - the museum takes it's name from his band, The Jimi Hendrix Experience).
Other fun stuff: offbeat items like the infamously diminutive Stonehenge model from This is Spinal Tap. Be sure and listen to the audio of Derek and David extolling the virtues of corporate sponsorship. If you don't know what or whom I'm talking about, either go rent the movie or, failing that, check out some of these clips from it, it's a comedy classic.