Concurrency and parallelism is hot these days and functional languages are superior there. Learning a different type of language will widen your horizons and on

Concurrency and parallelism is hot these days and functional languages are superior there. Learning a different type of language will widen your horizons and once you know one functional and one OO-language then it is quite easy to learn other languages after that. My suggestions are Clojure and Erlang. Both are made for cincurrency, have web frameworks(maybe not as good ones at rails though) and are functional. Both also run on a VM. Learning CLojure will also expose you to JAVA and the JVM.