I have posted some links on the side of this blog that will help you put together a free, first-class Lisp programming environment for Linux. It consists of SBCL, Emacs, and SLIME. I have been using this setup for a couple of months now and find it quite productive. I routinely have an SBCL session running in Emacs/SLIME for days, adding and correcting function definitions as my kids allow me some time. The links have a set of instructions associated with them. Note that SLIME isn't technically required. Emacs has a pretty good Lisp mode without SLIME but SLIME adds some productivity features that the basic Lisp mode doesn't have. The single biggest drawback of this setup is learning how to get productive with Emacs if you weren't already familiar. In short, Emacs is the most productive programmer's editor on the planet and is fully programmable in its own version of Lisp (e-lisp). Emacs and Lisp go together like peaches and cream.