Print out your research from the web

I love creating the perfect car online (complete with colors and other features).  I also find that these services often times allow you to price out your dream car (e.g., one with AC and one without).  This helps me figure out where the price differences are and I am much more prepared when I visit a dealer.  I once brought my print out to the dealership just to show what I had found.  It took a lot of the back and forth out of my purchase of my new Jeep!