I suggest Common Lisp. If you can afford to spend money go with Allegro Common Lisp or Lispwork. The best open source implementation is SBCL that works best on Linux. If you want to avoid commercial implementations don't expect any fancy IDE. You'll have to find what best suits you between Emacs and other alternative plugins for the most common open source text editors. If you are already familiar with Emacs then SBCL+Emacs+SLIME is a no brainer.