Check out
www.carbuyingtips.com. I dug around his site (avoiding most of the sponsorship), and learned quite a bit before I bought a used vehicle. He also has a bit of advice for new purchases as well.
Something else that I found helpful was
www.autotrader.com for price comparison. Most of the time you can find a pretty good deal in another area of the country, and have it shipped or driven to you. There are a few sites that will offer prices considerably less than dealers, but you can do the research there.
Good luck!