Just for fun, I want to try Common Lisp. (I’ve been using Scheme when I was a student.)
As an ancient language, CL has many implementations. Following Wikipedia, I chose SBCL, a descendent of CMUCL.
It it just like Eclipse for Java, Emacs + SLIME is powerful for Common Lisp (or Scheme). Auto-complete and other stuff are so well supported.
dpans2texi enables us to get help about the word under cursor by simply typing ‘C-h S’.