At the Powertoys Weblog, Sara Ford posted about a very cool tool which is available at gotdotnet: Regex Builder.
At gotdotnet it is described as follows:
A tool for building and testing Regular Expressions. It allows you to manipulate the expression and your source text, and shows you a tree with all of the Matches, Groups, and Captures found in the text.
I think this tool is easier to use for RegEx beginners than for instance The Regulator, because its GUI is pretty simple and there’s some standard information available at startup.