http://www.quora.com/Computer-Programming/What-is-a-good-way-to-debug-a-regex/answer/Scott-Danzig
This Quora answer kicks serious ass. Mentions a bunch of web resources that do a tough job amazingly well -- for an often-not-easy-to-please audience (Developers!)
Nice find!
I'm gonna repost this at work, great find
Yay, I win 9001 internets or something!