Whilst digging around earlier for various dot net stuff, I happened accross this open source regular expression designer on GotDotNet.
It's a WinForm app and allows you to create and test your regular expressions before using them in code (or your FlexWiki TopicIndex behaviour Ross)
Here's the home page of RegexDesigner.net
Regular expressions are notoriously tricky and hard to use, and this quote sums that up rather well (source):
Indeed, the syntaxical language of RegEx is as much intuitive as writing with my feet