>>12484076Arora Barak is standard.
Oded's book is also good.
This book I'm about to link below should be read alongside the the first as a wonderful way to learn how to solve nontrivial complexity theory problems - the book groups problems together by the techniques and ideas used to understand and solve them, rather than their field of incidence:
https://www.cs.rochester.edu/u/lane/=companion/Complexity has easy to solve problems and incredibly difficult ones without much inbetween, which I think it inherits largely from combinatorics and logic.
