A credit Union will get you the best rate by far, but getting approved is the problem. Dealers tend to have relationships with banks that can help you get in the door, though depending on the dealer, they can give you higher rates to make more money for the salesman, so be careful with that.
fun n sun just gave me a rate 2% less than wells fargo or texas trust credit union could offer. i checked other placed too but those are the 2 names i remember off the top of my head. i own my home and looked into a home equity loan which was 1% higher than the fun n sun rate.