Here's a collection of links to interesting intorductory sites and articles on color theory. I have attempted to provide brief annotations for each link. Those looking for a brief introduction that can be shared in class would benefit from Claudia Cortez's Flash animation project. Although a bit elementary, it is only about 10 minutes long and introduces many important core concepts. The Poynter Institute's Installation provides the most in-depth and sophisticated introduction (for those looking for something a bit more advanced).
I keep an active del.icio.us account as I troll the web. Here's some of the links I have bookmarked for color theory / tools / tutorials: