If you're really interested in calendars, the long awaited second edition of Calendrical Calculations is now out. It's 420+ pages with everything you ever wanted to know about calendars and a whole lot more. It's by Reingold and Dershowitz, Cambridge University Press, soft cover ISBN is 0-521-77752-6. 

This edition includes a CD with the code for the calendars in Java, LISP, and Mathematica.

(I have no connection, blah, blah, ...)

Dave