Which testing books are helpful in learning more about testing?

Cem Kaner, James Bach, Bret Pettichord: Lessons Learned in Software Testing. These testing books should be on any tester's desk - it's a set of 293 short pieces about different aspects of testing, from testing techniques to automation, to documenting your testing, to managing your career. It's probably the book that gets picked up most by colleagues (well, ok, the Manga Guide to Databases might just beat it, but that has the unfair advantage of being a technical book with a picture of a fairy on the front).

Jerry Weinberg: Perfect Software: and other illusions about testing. This is the book you want to get your project manager to read. Weinberg nails so many misconceptions that people have about what testing is, and what it can do for the project. Lisa Crispin, Janet Gregory: Agile Testing: A Practical Guide for Testers and Agile Teams. If you're working on an Agile team, you'll want to read this. Lee Copeland: A Practitioner's Guide to Software Test Design is the book to read on test design.