Some years ago I've been working just for fun on a simple VM that is able to run simple C# applications, that VM was able to run on old symbian phones with few resources.
When I've read the Arduino Due announce I've thought that is possible to run my VM on top of that hardware.
If you don't have any special requirement, C# might be rather good for simple things. Moreover the same executable can invoke a simulator if you run it on your computer while it can be used as it is on the real hardware.
These tend to use about 75% of their 512k flash for the .net microengine, which makes me sad. But given the fact that the remaining code space is still "large", and given the price point, I'm not sure that it should...
(huh. I've been going along thinking that Netduino and FEZ had a common origin, but it looks like they're quite different!)