I have been using a trial version of ReSharper for my DotSVN project and I should say that I just got hooked to it. I would not have made this much progress without it and that leaves me wondering what I would do once the trial expires!!
A tool with this ease of use is needed to improve the design and code without any hesitation to refactor.
ReSharper's code navigation capabilities are also extra ordinary. You can read more about it here.
I have also used dotTrace to fix a nasty performance issue.
Overall I am very satisfied with the product.