What languages are the most sought after from employers?

I'm wondering what languages are the most sought after by employers when it comes to what they look for in candidates.

I know that PHP is a common language, obviously!, and that a good developer can get a decent salary.

But what about other languages like knowing Perl or Python or perhaps something more lower level like C or C# or something like that: what are the hottest languages to know with employers and which ones are more likely to earn you more money.... I'm looking for something new to learn and would like to pick something that is attractive to employers so that I might even be able to get a better job out of it in the longer term!