Sipser, M. Introduction to the Theory of Computation,PSW
Publishing Company, Boston 1997. Third edition.
P, NP, and NP-Completeness: The Basics of Complexity Theory By Oded Goldreich, Cambridge University Press.
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
Computational Complexity: A Modern Approach 1st Edition, by Sanjeev Arora and Boaz Barak, Cambridge University Press.
The Nature of Computation 1st Edition
by Cristopher Moore (Author), Stephan Mertens, Oxford Press.
Here are links to some complexity course pages and notes
Professor Levin's Fundamentals of Computing
here and
here .