I would recommend

- Bargaining for Advantages: http://www.amazon.com/Bargaining-Advantage-Negotiation-Strat...

The very best negotiations book I have ever read.

Further, you should check-out the Harvard Negotiation Project: http://www.pon.harvard.edu/category/research_projects/harvar...

They do have nice and free reports on the different aspects of negotiations.

Let me know if you need further pointers!