I'm often in a position where I need to choose between a number of web technologies. These technologies might be programming languages, or web application frameworks, or types of databases, or some other kind of toolkit used by programmers. More often than not, after some doing research, I end up with a list of contenders that are all equally viable. They're all powerful enough to solve my problem, they're all popular and well supported, and they're all equally familiar/unfamiliar to me. There's no obvious rationale by which to choose between them.

Still, I need to pick one, so at this point I usually ask myself a hypothetical question: which one of these technologies, if I invest in learning it, would be most helpful to me in a job search?

Where can I go on the internet to answer this question? Is there a website/service that scrapes the texts of worldwide job postings and would allow me to compare, say, the number of employers looking for expertise in technology x vs. technology y?

(Where x and y are Rails vs. Djando, Java vs. Python, Brainfuck vs. LOLCode, etc.)