There are some good options. What do you want to learn? If you want to enhance your understanding of functional programming, go for one of the lisp-based languages. Emacs lisp is useful. Scheme is popular. There's always Common Lisp, of course. (Someone will say Haskell, but pick up a lisp-based language first before you tackle that, IMO.) If you're more inclined to shore-up your OO, go for Inform or Smalltalk. There are other options too of course. Assembly language is interesting to have under your belt; you won't use it much, but it's good background.