[gavinlynch]

I love these types of things. Kudos to the author.

This one in particular reminds me of a tool I've always found useful. It's an interactive Regex builder just like the one linked in the OP. I would say it's got some additional compelling features: like mouse-over breakdowns of each expression as you build it, a handy reference list as well, but also a community concept and saved expressions. Really, I've never found anything better. My only complaint is that it's flash-based, but it's an amazing tool, so can't really complain too much.

http://gskinner.com/RegExr/