I didn't like the butnth. I get an allergic reaction to append. Blame Ken Tilton.

  (defun shuffle-in-place (l)
    (cond ((null l) nil)
          (t (rotatef (nth 0 l)
                      (nth (random (length l)) l))
             (shuffle-in-place (rest l))))
    l)

  (defun shuffle (l)
    (shuffle-in-place (copy-list l)))