Question for functional fags

Many self-styled master programmers love to masturbate over LISP. Since there's probably something to it, I'd like to learn more about this eclectic pile of bracket fetishism; preferably Common LISP because CLOS sounds interesting.

I'm quite well versed in procedural and object-oriented programming, but my functional programming knowledge is more or less nonexistent. Can someone point me at a good book for learning Common LISP?

SICP SICP SICP SICP

Then you learn Common Lisp (Practical Common Lisp could be a good idea) if you want. But SICP is the source of all good.