I'm surprised no one here has mentioned the Cobra language (
http://cobra-language.com/). It's basically identical Python syntax that wraps C# and has almost
all the features Steve pointed out. It works on Linux, Windows, and Mac OS X using Mono (.NET environment emulation for various platforms).
Similar to JVM languages, it can import C# libraries directly and allows you to effortlessly use all that's gravy about C# but in a much more Pythonic manner. It has static and dynamic binding, which you can turn on and off, and since it's on Mono, does not have a GIL.
I think it's definitely a language to consider in the future. It certainly has potential to become the NBL.