In response to a question about handling money values in Lisp, John Wiegley mentioned his CAMBL project:
I have a written a library whose express intent is supporting monetary calculations in Common Lisp. You can even do multi-currency calculations, in which case "balance" objects are creating which track the individual sub-totals of each currency. You can convert between currencies using a conversion price, and track the history of known prices in order to support historical reporting of market values.
It's not finished yet, but sounds very interesting.