Cusp
Cusp is an Eclipse IDE plugin available from http://bitfauna.com/projects/cusp/index.html which runs on top of SBCL. There are builds for Windows, Linux and OS X (Intel) available.

(Note: It seems to be very difficult to find where to download Cusp at present. If you have trouble, use the following Eclipse update site).

Cusp is maintained by Tim Jasko

Project's site is cusp.devjavu.com

Article on CUSP at IBM Developerworks: http://www.ibm.com/developerworks/opensource/library/os-eclipse-lispcusp/index.html