I have the following installed:
- Imports Sorter (for VS 2005)
- GhostDoc
- Regex Find and Replace (.Net regex compatible find and replace, because VS has its own regex syntax)
- rockscroll
- Smart Paster
- Sonic File Finder
- Cool Commands
I have the following installed:
For Visual Studio 2008 I'd say PowerCommands is a must have.
I also use VisualSVN for source control.
Does F# class as a VS addin? :)
In all seriousness, ViEmu is the only addin I use.
I am totally addicted to all three, but if I really had to choose the most important one, I'd go with ReSharper.
CodeRush with Refactor! Pro
http://www.devexpress.com/Products/Visual_Studio_Add-in/Coding_Assistance/
Definitely Smart Paster