Nice little regular expression tester.
Regular expressions, if you are not a perl expert are often a pain in the ass to write, test and debug. Espescially if you are in python where there are a bunch of methods of doing extremely similar things, yet not quite the same. I found this really handly little regular expression testing tool, which runs off a web-browser and can run on your local computer called retest.
It uses ajax to make things simpler and more interactive and really useful if you are trying to parse really weird stuff.