Javascript is pretty hot right now with the advent of NodeJS. Scala and Clojure are the up and comers. Python is a solid choice. Java, C/C++ are classic and have some new features on the horizon. Haskell, Erlang, and other lisp varieties are enjoying a resurgence.

Those languages cover many genres of programs: Scientific, parallel/concurrent, server-side, client-side, desktop, mobile, embedded, scripting, business, gaming, and so on.

The question is what are you most interested in? Are you trying to find a job or are you learning because you find it interesting? Do you have projects in mind? What would be the right tool for the job?