Sipser, M. Introduction to the Theory of Computation,PSW
Publishing Company, Boston 1997.
Homer, S., Selman A. Computability and Complexity Theory,
Spring-Verlag New York 2001.
Garey, M., and Johnson, D. Computers and Intractability: A Guide to NP-Completeness, Freeman Press.
Papadimitriou, C. Computational Complexity Addison-Wesley Publiching Company, Reading 1994.
Lewis, H., Papadimitriou, C. Elements of the Theory of Computation,
second edition, Prentice-Hall 1998
Here are links to some complexity course notes
Professor Levin's Fundamentals of Computing
Lovasz: Computation Complexity (translation by Professor Gacs)