I’m a diehard ReSharper fan. I’ve had my own license for many years, and as far as VS has come over that time with refactorings and ease of navigation I still prefer to have the power of R# at my fingertips.
ReSharper 9 brings all new Regular Expression support: error and expression highlighting, four types of code completion, escape character help, and a very nice validation utility that lets you experiment with your expression on test input text against the .NET or JS regex rules, similar to the test capabilities in something like RegEx Buddy (which is awesome, btw), but built into VS.
DISCLAIMER: THIS IS NOT AN ENDORSEMENT OF REGEX! As the saying goes, ‘Some people, when confronted with a problem, think “I know, I’ll use regular expressions.” Now they have two problems.’ I fully subscribe to this, but I have to maintain a non-trivial amount of code with some hairy regexes and it will be great not to have a run a bunch of utilities or scripts to test something out quickly.