Reddit mentions of Postcolonial Theory: A Critical Introduction: Second Edition

I'm sure you'll get a number of recommendations for primary sources, but I'll just throw in my two cents on some quality secondary sources introducing the field.

Postcolonialism: An Historical Introduction, by Robert Young is excellent for a broad overview that looks at postcolonialism from a long historical perspective and across geographical boundaries (not just the narrow theoretical flourishing of the 80s and 90s).

Postcolonial Theory: Contexts, Practices, Politics, by Bart Moore-Gilbert is the best introduction to the "trinity" of Bhabha, Said, and Spivak.

Colonialism/Postcolonialism, by Ania Loomba takes a good activist and materialist approach to the subject.

Postcolonial Theory: A Critical Introduction, by Leela Gandhi focuses, as its title indicates, on the theory boom of the 80s and 90s, offering a look at its strengths and weaknesses as they seemed from an insider at the time.