I come from a background in C/++ with STL/ Win32 and MFC, and when I was told to learn C#, it seemed yuck. But I had to learn it , while at work, and now I find that C# can do stuff quicker than C++. And more over, C# is better supported by Microsoft in terms of usage with its future products, Offfice Development being an excellent example. Not that Office Development cant be done in C++, but C# makes it much easier to . So learning C# is advantageous . I cant comment on Java, as I have never worked on that , but .NET has its Java counterparts.
But Python should be a must on your list, it is easy and very powerful . I started with Python, and found it easy to pick up . Python has C# and C++ bindings and though I am not an expert in Python, but I see there is lots of potential in it.