Anthony Zee's book QFT in a NutshellQFT in a Nutshell is remarkably complete, and yet rather small. It provides a good intro to the subject.
A complete, thorough and good book is Steven Weinberg's 3-volume opus on QFT 3-volume opus on QFT(vol. 1, vol. 2, vol. 3). It is perhaps tootoo complete for beginners.