I got my car from a dealer. They wanted $19k so I told the salesman I didnt want to spend over $15k. He came back out 5 mins later and said I could have it for $16k driveaway. So I saved $3k (15% in 5 mins.
Dont be afraid to push them hard to get a good price, but be nice about it, and dont make it too obvious that you really want the car. Kinda give them the impression that if their price isn't good enough, you'll happily go find another one.
If its been on the lot for a while you are more likely to get a good price too I would think.