Here we go, I release the first shot of a tool I start writing months ago... The goal of that tool is to find some strings that are valids and which pass your regular expressions filters. Basically, it was designed for testing IDS regexp.
The tool is not finish yet, I have lots of work to do on this, especially the attack strings dictionary; currently there is only some client-side string patterns.
You can download the tool here: RegFuzzer

For using the tool, you need to enter the regular expression to test into the XML input file, and launch the tool like:

python regFuzzer.py -f input.xml

This will produce an HTML file as output. As I said before, this is the first release the goal is much more to show that tool and see if the idea is interesting for you; if so, I may work more on this. Don't hesitate to drop me a line about the tool if you have some comments.