In december I’ve wrote an article talking a little bit about color theory and featuring Kuler, a very nice and useful tool from Adobe to explore the color theory.
Now, reading the Usabilità blog I came across with a nice tool that is much simpler, but has the power to bring insight when choosing colors for web pages. Also has the advantage that no much color theory is needed to use it. Very useful tool.
If this appeals to you, check Yafla.