From what I've heard, summer is the worst time to buy. Salesman told me that's when everybody wants to buy a new vehicle during the summer so they are less likley to deal because they know they will get buyers regardless. Check out
www.edmunds.com. They have a lot of great info on there about buying new vehicles (invoice price, holdback, dealer cost, and when rebates are offered). Also a few great articles on how to negotiate. It helped me out when we got my wife a new SUV. Also, get a bunch of online quotes from dealerships. I printed out prices and got the local dealership to beat the lowest one by $1,000 with added leather. It came in almost $3,000 under invoice price (not sticker price).