A comprehensive reference--lots of information here--a good place to start. Encyclopedia Mythica
A bit more sophisticated, this website moves beyond the basics. The Greek Mythology Link
Animated myths, gods, and heroes Myth Web
Fun and interactive site (with Hermes as your guide!) Both Flash and HTML versions available. Mythology Fun
Helpful page for pronunciation of Greek names, etc. Pronounce it right!
Myths (the actual stories in a shortened form) MythMan.com
Some related material (including constellations) More Mythology Stuff