Winged Sandals - from the Australian Broadcasting Corporation and University of Melbourne's Centre for Classics and Archaeology
This is a little slow to load, but pretty cool. Once you get into it there are a few sections.
Theoi Greek Mythology - This would be a good site for research. There is a lot here but it's pretty clearly and attractively organized and appears to be high quality.
Ancient Greek Mythology - A lot here, a bit overwhelming, but could be a good jumping off spot for finding resources for students. The copyright notice is from Anthony Bulloch and the U.C. Berkeley Dept. of Classics. Don't know if he's a professor or student.
Greek Mythology.com - has information on all subjects of Greek Mythology, including details on Greek Gods and Greek Goddesses, Greek Myths and Greek Heroes like Achilles and Hercules. It also has full text of Greek Mythology and Literature books. Easy to read and access information, but unclear who is responsible for it.
In Search of Myths and Heroes - PBS series
Includes Jason and the Argonauts, along with King Arthur, Shangri-La and Queen of Sheba.
Greek Mythology Link - Looks quite academic and reliable, but a bit tough to wade through if you don't know what you're looking for.
Website run by a teacher from Athens, Greece. Information in this website primarily taken from ancient Greek writings; some is an amalgamation of various myths. "Please don't view the material as being from an authoritative source, since I am only a hobbyist in Greek Mythology."