A couple of days ago Packt released the results of their 2016 Skill Up survey and it is well worth a read!
There's not much point in me going in to detail but one thing that surprised (perhaps it shouldn't have) was that "Bash, Perl & Scala come out as the programming skills commanding the highest salaries.". I am not sure why, maybe because I work primarily in a .NET environment, but I didn't expect that.
Something that didn't surprise me is that Python, once again, comes out as one of the top skills to have. I love Python but, although I agree that it is, I think that devs who buy from Packt might often do so because of their Python library and this might skew the results.
As they usually do when releasing the survey Packt have also have a sale on all ebooks and video courses. Each being a tenner it is well worth checking out. They even have a handy list of their Top 20 and some preprepared bundles.
And I just want to say, although this might read like an advertisement I actually have a paid subscription to Packt's Mapt (which is also worth checking out) and I really find their material to be of excellent quality.
So go Skill Up!