When working with RegEx editor in Visual Studio, ita takes a lot of thinking and testing to find out actually if your expression is working. Sometimes you need to run the entire code or at least a test page to get it right.
Visual Studio gallery has a new tool, RegEx editor which has its own editor for regular expression and ability to test sample data along with colorization, brace matching, sample testing grouping and choice tracking. Download it from here. ( It works with Visual Studio 2010 )