[mindvirus]

My three cents:

1. Learn bash. It's the glue of the *nix world. It's not complicated but it's foreign enough that it's worth spending a few weeks really understanding.

2. Learn Javascript. It's the C of the modern era. Practically every piece of software in the world has to interact with Javascript, and the value of it is only increasing.

3. Learn C. It's the Javascript of the old world, and the foundation on which most of modern computing is built. If you need to get two things to talk to each other, the answer is usually C. Fortunately unlike its younger brother C++, it's a fairly straightforward language to learn.