Dealer Holdback
There's something called "dealer holdback". There's a website that gives the amount or percent of holdback by Manufacturer. Here's a writeup on it from the Edmunds site. [link|http://www.edmunds.com/advice/incentives/holdback|Holdback]
Usually, $100 over invoice is about as good as it gets, unless you find a day that noone is buying. A very wet, bad weather day. If the dealer hasn't made their sales quota, end of month can be promising, too.
My wife is the queen of negotiations. She won't buy unless she's in the holdback. My mother had a deal on a used car about 2 years ago. Before she said "yes", she called my wife and my wife managed to get an additional $2000 off of the deal.
Glen Austin
