My favorite, all time Visual Studio add-in is DevExpress’s CodeRush. I haven’t had time to do a good blog entry on it, but if you are looking to buy yourself a Christmas gift, this would be an excellent choice. (http://www.devexpress.com/Products/NET/IDETools/CodeRush/Index.xml)
DevExpress’s CTO of developer tools and grand poobah of programming is a C# MVP named Mark Miller. Mark has made many appearances on Dot Net Rocks (http://www.dotnetrocks.com) and DNR TV (http://www.dnrtv.com). His appearances are always informative and educational. He has a unique way of looking at the world that will make you think about programming (and other things) in new ways.
Mark just blogged (http://www.doitwith.net/2006/12/23/ChristmasCancelledAgain.aspx) that he’s got a quick feature he’s adding to the new version of CodeRush, and there’s a possibility it could be ready for Christmas Day.
Yes Virginia, there is a Mark Miller!
UPDATE: I finally got around to writing about CodeRush, you can read it here:
Arcane Code 
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