I'd previously used the free version of Refactor for VB.NET and found the addition of a refactoring tool extremely useful when coding.
One problem I did notice that Visual Studio seemed to crash and hang reasonably frequently. I originally put this down to running Visual Studio 2005 on Vista, but with the Visual Studio service pack and extra patches for Vista compatibility on Vista, this became less of a suspect.
More recently I ran a 30-day trial of ReSharper. It does most of the same refactorings as Refactor, but I didn't notice the stability problems. It seems quite capable, and also offers academic pricing which makes it very competitive.
Another thing that has impressed me about ReSharper is that they are quite responsive to bug reports - I spotted a few issues during my trial and they have a nice transparent system for tracking the reporting and fixing of issues. You can even download their latest internal builds directly (at your own risk)
I then began a trial of the latest version of the full commercial version of Refactor. They have 2.2.2 downloadable for evaluation, but it turns out this version doesn't include the ASP.NET refactorings. An email to their support address gave me access to 2.2.4 which comes with the ASP.NET bits.
Sadly, the evaluation only went down hill from there. Visual Studio repeatedly froze. I've sent of another query to their support and maybe there is a workaround, but for now it appears that the instability is a show stopper.
It's a pity, as Refactor does have quite a few more refactorings than ReSharper, and I think their refactoring interfaces are a bit slicker.