Yahoo's Toyota-Prius group is a mainstay of the Prius community.
www.priusonline.com is an up-and-coming commercial free Prius site.
priuschat.com is another new prius discussion site.
Lot's more Prius Accessories are available at Coastal Electronic Technologies.
A totally obsessed Prius Owner's website.
Another Prius owner with great information on how the Prius drivetrain works.