phpguru.org - PCRE Cheat Sheet:

Inspired by the great stuff at ilovejackdaniels.com, here’s a dedicated PCRE cheat sheet. The PHP cheat sheet at ILoveJackDaniels is fine enough, but PCRE goes way beyond what is there. Hence, this. Enjoy.

This is a handy little sheet. Print it out and tack it to your cubicle, code monkey!