Books that should be part of every web application security tester's library, especially for using Burp Suite:
If you are a web application penetration tester, you should get the Web Application Hacker's Handbook, Dafydd Stuttard and Marcus Pinto, Wiley. This is the de facto book on web application security.
Get the Instant Burp Suite Starter, Luca Carettoni, Packt Publishing, to get started quickly on using Burp Suite.
The Tangled Web: A Guide to Securing Modern Web Applications, Michal Zalewski, No Starch Press. He is the author of the extremely informative Browser Security Handbook as well: https://code.google.com/p/browsersec/wiki/Main.