Just seen at Larkware news. JetBrains have a new version of Resharper. This is for VS2005 only.
There has been a Unit Testing tool inside Resharper for the last version or so. JetBrains have now decided to offer this unit test runner as a free addin .
I have downloaded the new version but have not checked it out yet.
On the subject of cool addins for Visual Studio . Mark Miller has indicated that a new version of code rush is coming soon. Although his metrics are a little interesting.