The VS2008 development tools for Silverlight 1.1 have been re-released and now work with the release version of VS2008. The tools ad-on can be downloaded from here.
Visual Studio 2008 Shell
Do you have a burning desire to develop your own IDE? Perhaps you have an amazing new feature to add to VS200? Either way, Visual Studio 2008 Shell may be just what you need. It comes in two flavours: integrated mode and standalone mode. In the first case, it is effectively a development framework for your amazing new feature that enables it to integrate seamlessly into VS2008. In the second case, it is the skeleton of an IDE that you can customise to your requirements and re-badge to fit your brand image, rather than Microsoft’s.
You can read more about it here.