As I’m sure you’ve heard, we’re done! And you can download everything at your pleasure. Visual C# Express 2010 is available for free at the following link. For free!
You can also download trial versions of the full Visual Studio SKUs from here:
MSDN’s main page is covered in purple and full of more links than you have time to click on, so you can check out everything there too.
The C# compiler and the support for dynamic, including the DLR, come in the box on every distribution of the .NET Framework 4.0. And also, of course, with every edition of Visual Studio. In addition to that, you’re going to want to use C# dynamic with some good dynamic languages. Happily, IronPython has released a final version (2.6.1) built for use with .NET 4.0. Check it out!
UPDATE: It wasn’t up when I posted this, but now IronRuby has also pushed a final build (1.0) that runs on top of the released .NET 4.0!