More great advice!
I'd also advise you to walk away from the car you want and come back the next day. That gives you a chance to reconsider your decision and makes the salesman sweat a little bit. Sales guys hate investing their time and then losing the sale. If you make him sweat for 24 hours, he's more likely to give a little. Also, if you aren't pressed for time, consider shopping at the tail end of the month. Nothing makes a sales guy happier than getting a big commision in under the wire. They often have bonuses based on monthly sales totals and are a little more flexible on the 29th of the month than they are on the 1st.