I suggest you the book "Nonlinear Dynamical Systems and Control: A Lyapunov-based approach" by W. M. Haddad and V. Chellaboina. You can take a look inside at amazon.com.

"Nonlinear Systems", Prentice Hall, Hassan K. Khalil. It has a solid theoretical background but you may not find some of the hot topics.

Thanks a lot to all...But, I think these books are very costly! Aren't they?

Yes, they are. But you can buy it all at www.amazon.com as used books, sometimes you will find it more cheaper. Or try at www.abebooks.com

Bocalleti et al did a good job in a publication (i can send it as soon as i find it) which summarizes nonlinear systems and control methods. I'll try to send some other materials

S. Boccaletti et al. / Physics Reports 329 (2000) 103}197, Physics Reports 366 (2002) 1–101 and the references therein.

Thanks a lot!!