ReSharper by Jetbrains
I finally managed to have my Addins in Visual Studio .NET 2003 working again, with reinstallation of it and then running a repair.
Then I installed ReSharper 0.81; I am part of the Early Access Program, and worked with it for a couple of hours. There is much more features then the older version I tried, and for the moment I am happy with it. It brings lots of added value that will be present in Whidbey in Visual Studio .NET 2003.