www.edmunds.com is the best that I've been to.
http://auto.consumerguide.com is pretty good also.
Unfortunately both of them don't go back very far, just into the early 90's. I haven't found any good general car repair stuff online unless you search for the specific repair you need to do in google. I just have a Haynes manual for my car and anything that I think I'm ill-equipped to do I take it to the pros.