F#. It should let me get my mind around a somewhat different approach to programming compared my main languages (C#, Javascript) while letting me still work with a know platform.
+1 for F#. it is a really great language and I learned a ton by spending about 250 hours with it. The book Expert F# is a really good resource. the first 200 pages are about the language (a complete guide) and the rest is just case studies of .NET junk. I wish they had made 2 books not one... 1st 1/2 is excellent though and worth buying.
