My license for Whole Tomatoes Visual AssistX is about to expire and I'm not really planning on renewing it. I use it for spell checking but that's about it. The refactoring abilities have been a little disappointing. Before I just jump into Resharper though what are your thoughts on other possible plugins?
The other major player would be DevExpress and their CodeRush and Refactor products. Found here.
Aside from trying out Visual AssistX, the only other one I've tried is ReSharper (which I highly recommend). If you do decide to go for ReSharper, you'll likely notice that it's missing a spell checker for code though - however the Agent Smith plugin fixes that.
I'll repeat my answer from Essential Programming Tools.
.NET Dev:
* Visual Studio 2008 (can target .NET 2.0 - 3.5) * Resharper * MbUnit (backwards compatible with NUnit) * FogBugz for work tracking * Subversion for source control * Red Gate SQL Toolkit * Google * Rhino Mocks * Nant * KDiff for diff/merging * MS SQL Express (or go Developer Edition if you have MSDN)
You should take a look at Visual Studio Gallery, the one stop shop for Visual Studio extensions.
Here you'll find quite a lot of extensions for Visual Studio in all categories, from intellisense and refactoring to designers and documentation builders.
Once you get into resharper, you really don't want to leave, its done a massive amount to improve my productivity.
It depends though on what you are doing. Are you doing a lot of TDD when you write tests, write code, then refactor?
Unless you are pretty intensely into refactoring then I'd suggest that you might not get the best of out R#.
As a plugin for a plugin I use the RGreatX plugin for R#. It's really handy for shifting string values out to resource files for localization of the software.....saves me plenty of time!
Have you tried model maker code explorer?
It is a great tool in delphi and the visual studio version looks pretty sweet as well. Still trying to work out what the best option for VS is though.