Two interesting books / resources tips:
The book is in German, but a English version is apparently coming out soon.
The website also contains a large amount of Processing code examples:
(via Till Bovermann)
“This is the official on-line repository for the code from the Graphics Gems series of books (from Academic Press). This series focusses on short to medium length pieces of code which perform a wide variety of computer graphics related tasks. All code here can be used without restrictions.”
(via Dave Griffiths)