Regular expression tester
Regular expressions are the bain of my existence when it comes to DTb. This isn’t because of any particular failing in DTb – Andy has made it extremely flexible by allowing regex. Mostly it’s because I don’t have a lot of experience with using them (beyond the occasional search in TextPad), and I didn’t have a way to easily test and troubleshoot them.
Well, gskinner to the rescue with a web app for this (Flash required). There’s also a desktop version (Adobe Air required).
There is also a good guide from Jan Goyvaerts.

This one is no bad. Online, javascript, and all.
http://www.pagecolumn.com/tool/regtest.htm