Albert is a Common Lisp doc-generator, comparable to Javadoc and Doxygen. Currently it generates DocBook. It reads an ASDF system definition and documents the system. It has been an experimental system that I've used for my own projects, but others have found it useful too. Give it a go and let me know what you think.
ASDF-install package (obsolete) http://albert.sourceforge.net/albert-0.4.10.tar.gz