Learn three or four languages. For truly heavy computations and for serious scientific programming you really ought to learn C. It's also the de-facto gold standard of the computer industry. Chances are whatever computer you're on is running hundreds of thousands of lines of C code at this very instant. There's no shortage of freely-available learning material out there, and it's a skill you will never regret having acquired.
Unfortunately, your question is a little bit like: "which tool should I learn to use-a hammer or a drill?" The answer, of course, is both. I'd recommend you start with C and then broaden your field of view with something like this: http://pragprog.com/...-in-seven-weeks
Disclaimer: I'm a software development consultant by trade, specializing in systems integration and commercial websites and applications. I've been paid to write code in C, C++, C#, Visual Basic, Java, Ruby, PHP, Perl, Python, and Javascript.