Structural Complexity I (Texts in Theoretical Computer Science. An EATCS Series)
Jose L. Balcazar, Josep Diaz, Joaquim Gabarro
If you are learning about complexity theory for the first time, I recommend you read Papadimitriou's excellent book on the subject. One aspect about this book that I did not like is it's lack of combinatorial analysis, and its more generic, structural apporoach (i.e. focusing on robust sets of problems). Some may prefer this, but I think the combinatorial approach is more in line with mainstream computer science.
