That probably much depends on what you are doing or want to do, and to chose a language that best complements what you already know. If you want to make safe bets, pick one from the "most popular" chart that you did not list (JavaScript, Python, C#, Perl, and Ruby). However, some more exotic ones might be worth your time, too: Scala might become more important in the future, for example, as it offers concurrency support. Same for Clojure that has some popularity on HN at least. On Erlang I probably do not need to comment, either. An if you work Apple stuff, Objective-C, naturally. If you go into games development, Lua is an option. Etc., etc., etc. In essence, it is not very hard to pick up a new language - the real work is knowing an important framework that the language provides really well; Which ties in with what you want to do with it in the first place, again...

EDIT: And one more thing occurred to me: With NoSQL loosing popularity currently, I think having good SQL skills will be of more value once again. And, truly efficient DB management (and design) cannot be done from some ORM alone; designing well-formed Schemas and writing good SQL (or knowing how to use an ORM to produce the "right" SQL) is an art that should not be underestimated.