There is always more to learn about negotiation. In order to keep learning, take a look at the following resources:
Cohen, H. (2006). Negotiate This!: By Caring, But Not That Much, Business Plus.
Diamond, S. (2010). Getting more: How to negotiate to achieve your goals in the real world, Random House/Crown Business.
Fisher, R. & Ury, W. (1991). Getting to yes: Negotiating agreement without giving in, Penguin.
Mnookin, R.H., Peppet, S.R., Tulumello, A.S. (2004). Beyond winning: Negotiating to create value in deals and disputes, Belknap Press of Harvard University Press.
Shell, G.R. (2006). Bargaining for advantage: Negotiation strategies for reasonable people (2nd Ed.), Penguin.