Another good website for car buying is:
http://www.edmunds.com/
It has both new and used advice. It has a section on dealer tricks / do's and don'ts. I have used it for the last two vehicles I purchased. It also has a section that provides "what others are paying" based on zip code.
Wee Hooker is right - if they are still happy with you after the deal you payed too much. I was able to frustrate the salesman to the point where he visibly showed it when I purchased my truck. Even with all that - you still tend to feel 'violated' after the deal.
Like everyone has already said - get everything in writing - one of the forms, don't know which one has a place to write things in. Make sure you write in everything you want. Take the time before you go in to deal and make a list of what you want. The dealers will spin you around and confuse you during the deal. You at least have a fighting chance if you have a list ot refer to. I even wrote that I did not want the dealership sticker on the tailgate (free advertising!)
best of luck