recur
RECUR is a convenience library that contains the RECUR macro for named-LET style functionality, written by Robert Smith.

RECUR can be downloaded with Quicklisp, and the source contributed to/viewed here.

Example usage:

(defun factorial (n)
  (recur fact ((n    n)
               (prod 1))
    (if (zerop n)
        prod
        (fact (1- n)
              (* n prod)))))