[mheathr]

Lispworks is an excellent commercial IDE as well, however its editor is not as nice (but similar to Emacs) as using Emacs itself and the license is quite expensive compared to other IDEs/toolchains, but it offers greater code introspection than what is available in SLIME.

Personally, I use SLIME + Emacs as I do not do enough CL development to warrant dropping over a thousand USD for a license and I find SLIME good enough for my usage.