From dozens of cool PDC 2008 videos there are two I obviously like the most:
The CLR has great support for dynamic languages like IronPython. Learn how the new Dynamic Language Runtime (DLR) adds a shared dynamic type system, a standard hosting model, and support for generating fast dynamic code. Hear how these features enable languages that use the DLR to share code with other dynamic and static languages like Microsoft Visual Basic .NET and C#.
IronRuby is a new dynamically-typed language for Microsoft .NET that offers more runtime flexibility at the expense of compile-time verification. Find out why this is a good thing in the right situations: static compile-time verification for components that need additional rigor, and dynamic typing for more fluid parts of a program. See how to use dynamic typing to create internal Domain Specific Languages (DSLs) and how to use them for systems that you create.