IronPython Tools for Visual Studio
Whilst there have been many good IDEs with IronPython support there has until now been lacking from Visual Studio - and adding support has been the highest voted Visual Studio feature request for some time.
Adding good support for a dynamic language to an IDE is very different from supporting statically typed languages. The internals of Visual Studio rely on the static type information for the intellisense, designers, refactoring and so on. However, the IronPython team themselves have come to the rescue and built IronPython integration into Visual Studio 2010: