There are usually some pretty great lists posted by the IEEE and other organizations showing trends on languages year over year. If you're looking to score a more corporate style programming josb, especially in larger companies, the bigger languages are usually ones like C# and Java.
If you're looking more toward mobile development, you'll need C#, Java, and Objective-C.
If you're looking more toward web development, PHP and JavaScript are by far the the best to know (in terms of number of jobs out there), but Java, Python, Ruby, etc. are all out there to a lesser extent as well.
Newer languages like Python, Ruby, Haskell, GO etc. are all available, but in much smaller numbers. Usually more leaning towards smaller companies or startups who have the luxury of starting projects from scratch and not having to work with decades of legacy development. Although, there are obviously exceptions such as Google programming a lot in Python.
Learning the first programming language is the hardest. After that, most of them are just a variation on how you do things, but the flow is the same.
My suggestion would be that if you already know PHP, maybe learn something more traditional like Java, C++, or C# so you have a bigger breadth of knowledge and are open to a wider range of jobs. Ruby on Rails is very similar to PHP in the types of jobs that would require it. So, unless you are specifically really, really interested in only web development jobs, I'd suggest mixing it up a bit.