I'm looking for clean, well written Common Lisp code for the purpose of studying it. I started learning Common Lisp recently and feel that looking at how other people do things would be greatly beneficial but I don't want to acquire bad habits by learning from crap which is why I'm asking.
If you want to see Read some implementation's code, like SBCL or read some libraries code, like CL-PPCRE, or read some Symbolics code (OpenGenera) if you wish, or CL-HTTPD or similar.
There's also a lot of good books which you might want to read, like Practical Common Lisp (the style presented in this book is very good), or PG's "ANSI CL" or "On Lisp"(the style isn't bad, but it's not typical CL style, it's quite Scheme-ish), PAIP (quite reasonable style, but it does use some hacks here and there for didactical purposes), and of course, ClTl2 and the Hyperspec.
There are reasonably well-kept coding conventions which have survived through the time, so if you need to know if some habit is good or bad, ask in c.l.l or #lisp, altough I think everyone has their own quirks when writing Lisp code, or code in general.