[hga]

If you don't think you've mastered "Lisp" yet, you could do worse than one of the two lower level ones, Common Lisp or Scheme. In a lot of ways they're close to the machine while still giving you all sorts of nice high level stuff.

However, looking at what you've done so far, you could do worse than getting a good mastery of C. It's a descent "smart assembler", it's not all that big as a language (plus the minimum of the standard library), it's good about teaching you concepts that are close to the machine and it's a common base for a lot of the higher level stuff that you've used or played with.