I will rule out C#. C# never really took off and hardly is the Java killer that it was touted to be.
Never really took off!?!? What planet is this guy living on? Most new Windows software by companies other than well-establish C++ workhouses + all indie work is being done in C# these days.
C# is more fun to work in with each release, as Microsoft courts programmers who can tell a closure from a hole in the ground. Unfortunately, it has a rather anemic community compared to many other languages.
You're looking at github, which is primarily for open source hackers...... most whose work isn't on Windows. While GitHub is representative of hackers' language preference, it's not representative of language popularity. You need to keep in mind that C# is really (mostly) a Windows-only language, and open source tends to be much more proliferative on non-Windows platforms where Java is a much more feasible option.
But, yeah, C# is becoming more and more exciting with its new anonymous methods, lambda expressions, and more :)
Github is probably representative of C# and Java among hackers.
But it isn't representative of hackers language preference for all languages. Github will almost certainly underrepresent both python and haskell, and bitbucket will overrepresent python.
My impression is that the Haskell community is tired of the lack of github-like darcs hosting, and are switching to Git for github. After all, you can losslessly convert between Darcs and Git, so even though the code is on github, they may be typing "darcs ..." to work on it.
Never really took off!?!? What planet is this guy living on? Most new Windows software by companies other than well-establish C++ workhouses + all indie work is being done in C# these days.