I was checking out the winners of this year's Webby Awards and found some really fascinating stuff I hadn't encountered before:

Plumb Design Visual Thesaurus - Offered in both an online and desktop format, this reference tool gives you a manipulable graphical representation of your selected terms, allowing you to explore interrelationships between words. Really engaging stuff.

BrainPop - An educational site filled with great animations, quizzes, games, etc. There are many sites that work in the same domain, but this is amongst the elite.

Theban Mapping Project - Working toward a comprehensive archaeological database of Thebes. Be sure to check out the Atlas of the Valley of the Kings - a genuinely worthwhile timesuck.

There are many other sites worth exploring amongst the nominees, so check it out.