Emacs... Largely written in Lisp and is a great resource. Also has SLIME which is a fantastic way to develop with Common Lisp. Clojure support in Emacs (via

Emacs... Largely written in Lisp and is a great resource. Also has SLIME which is a fantastic way to develop with Common Lisp. Clojure support in Emacs (via Cider) is also great. Emacs is often the first exposure that many get with Lisp (other than SICP). In terms of nice Lisps to work with I think Clojure is more active as a community than any other dialect, and so it's useful for contemporary projects and generally getting help and support and so on.