I was in your same position about a year ago. My best advise is to shop online and get bids on the cars you want and then find the car at a dealership by you and negotiate the price you got online.
Here is a great website that walks you through the process. I thought it was the most helpful site b/c it has links to all the others and also walks you through the basics of the negotiation process.
Whoever mentioned carmax is also right on the money. I sold them my old car and they gave me about $1000 more on my old car than people were offering me on a trade-in (I didn't have time to sell my car).
Good luck and feel free to PM me if you have any questions.
LD