Regular expression tools

There is a nice set of tools that may be of great help for anyone working with regular expression on the .NET platform.
Following is a list of some of these free tools:

RegexDesigner.NET (full C# source code available for download)
Rad Software Regular Expression Designer
Expresso 3.0 (the source code for an older version of Expresso can be freely downloaded from the CodeProject site)

Finally, if you need regular expressions reference documentation, examples, tutorials, etc. to start out, is probably your site.