I am a corporate C# programmer. I found some time to invest into myself and stumbed upon a dilemma. Where to go from now? C#/.NET is easy to learn, develop for, etc. In future I would want to apply to Microsoft or Google, and want to invest spare time wisely, so what I will learn will flourish in future.
So: Python or C++ for a C# programmer? I am a little scared of C++ because developing anything in it takes ages. Python is easy, but I take it as a child-play language, which still need lots of patching to be some mature development tool/language.
Any C# developers having same dilemma?
C# is a little closer to Java and C++ than it is to Python, so learn Python first out of the two.
However, my advice would be:

Stick with your current language and learn more techniques, such as a wider range of algorithms, functional programming, design by contract, unit testing, OOAD, etc.
learn C (focus on figuring out pointers, multi-dimensional arrays, data structures like linked lists, and resource management like memory allocation/deallocation, file handles, etc)
learn Assembly (on a modern platform with a flat memory architecture, but doing low-level stuff like talking to hardware or drawing on a canvas)
learn Python or Ruby.  Chances are, you'll stick with one of these for a while, knowing all of the above, unless some hot new language has come along by then.
C++ or Python for C# programmer?