I'd say JS is by far the hottest language around and I'm a ruby programmer not JS programmer (although, I'm starting next month with JS).
Then depends I guess:
* if you're a web dev, JS/RoR/SASS/HTML5 with an eye on Rust and Go. Python has interesting frameworks also for web-dev.
* If you're into mobile Java/C++/Obj-C of course (old news) and HTML5
* If you're into low level, embedded stuff it's always C.
* Scalability? Erlang... and so on..
It's really easy to follow the trends around. The hard part is to understand new trends well enough in order to be able to understand if they are a better fit and use them in production. (e.g. Go is faster than RoR, but most people will stick to a framework that's heavily tested, well supported, with an active community, huge set of external plugins and tutorials .. for production. This might change in 4 years... Or maybe not :-)