C# 4 d:

[DreamThrall]

http://blogs.msdn.com/ericlippert/archive/2008/10/28/the-future-of-c-part-two.aspx

http://blogs.msdn.com/cburrows/archive/2008/10/27/c-dynamic.aspx

Also, I understand this will be a part of it as well: www.codeplex.com/MEF

I'm pretty psyched. Discuss (if you're one of the handful of people here that use C#)!