The new version of the Visual Studio 2008 Beta2 SDK was just released. Among the many new samples is a basic expression evaluator sample. This sample shows you how to add basic debugger support to a managed language in Visual Studio.
This is the first version of the sample and mainly has support for locals and member expansion. I'm planning on adding more features in future releases. Since this is mainly to provide users with guidelines on how to build an EE, any requests we get will be given a lot of consideration.