Interactive regular expression constructors
I love regular expressions. Any tool that helps me more interactively construct my expressions is a Good Thing indeed. I thought I'd list some of the tools I use for those that might not yet be aware. Note that these tools don't attempt to help teach your regular expressions; however, they could almost certainly help in the learning process.
All the tools below support what I consider core features: the ability to specify match options, the ability to perform a match or a replace, and the ability to display matched groups in the results. Each respective tool has its pros/cons, and each has some very creative features. Rather than provide a breakdown of the features for each, I suggest you try each independently and decide which works best for you.
Chris Sells' RegexDesigner.NET (Source code)
Darren Neimke's RegexSnippets (Source code)
ActiveState's Komodo (an IDE, but a great regex toolkit is included)
The Regex Coach (Tim Tabor posted this in the Win Tech: Off Topic list today)
All of the tools are free with the exception of Komodo. If anyone is aware of any other tools similar to the above, please let me know.