An ifixit[0] like site for repairing your car. I really like the format of ifixit because they give detailed pictures and the tools you will need. A site like this would be great for cars, ranging from just changing oil and tires to possibly harder things.
[0]: http://www.ifixit.com/
EDIT: If you create the site, please let me know. This is not something I can work on right now but if it's a wiki like site I'd love to contribute.