What I'd really like to attempt is a port of MockMaker
to .Net. That would be interesting.
One thing I've noticed is that porting heavily test-covered code is incredibly easy. It helps that C# resembles Java's long lost twin brother in many ways. What's really good is that the test code can generally be copied almost verbatim as it tends to be quite simple, and it lets me drive the production code into existence in the .Net idiom, as I'm duplicating the intent rather than simply pasting Java into C# and fixing all the syntax errors.