Support your local dealer! If you, however, buy those books through Amazon after following the links to the Amazon website, you support the FLOW3 development by donating to the TYPO3 Association.
Any book you buy can help, if you use this link to the Amazon website first.
Thanks!

We have read a lot of books (and still continue reading...) while working on FLOW3. And whenever we recommend some in some presentation people seem eager to read those books, too.
Ok, here is a list of the things we can recommend heartily.
Applying Domain-Driven Design and Patterns
by Jimmy Nilsson
RESTful Web Services
by Leonard Richardson and Sam Ruby

JavaScript
The Good Parts
by Douglas Crockford
Refactoring
Improving the Design of Existing Code
by Martin Fowler
Clean Code
A Handbook of Agile Software Craftsmanship
by Robert C. Martin
Test Driven Development
By Example
by Kent Beck
Continuous Integration
Improving Software Quality and Reducing Risk
by Paul M. Duvall
Design Patterns
Elements of Reusable Object-Oriented Software
by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides
Patterns of Enterprise Application Architecture
by Martin Fowler
Enterprise Integration Patterns
Designing, Building, and Deploying Messaging Solutions
by Gregor Hohpe and Bobby Woolf
xUnit Test Patterns
Refactoring Test Code
by Gerard Meszaros