This isn't exactly an answer to your question, since you asked for just one programming language, but there is a book coming out soon (pub date listed in Amazon

This isn't exactly an answer to your question, since you asked for just one programming language, but there is a book coming out soon (pub date listed in Amazon is Nov 10th) entitled "Seven Languages in Seven Weeks: A Pragmatic Guide to Learning Programming Languages". It's written by Bruce Tate (author of books on Ruby, Rails, Java, etc), and published by Pragmatic Programmers. The book covers Ruby, Io, Prolog, Scala, Erlang, Clojure and Haskell, spending presumably, a week on each. According to the book description, "you'll explore the most critical programming models of our time". This would seem to be a good way to learn about a lot of different programming languages, in a relatively short amount of time. Of course, if what you want is something that will be immediately useful on your resume, this may not be of interest to you right now.