Can you recommend any books on the Hebrew Calendar or Jewish Holidays?

For a good reference book on the major Jewish Holidays, I’d suggest Michael Strassfeld’s The Jewish Holidays: A Guide & Commentary.

Rabbi Nathan Bushwick’s Understanding the Jewish Calendar explains some of the mathematical and scientific underpinnings of the calendar.

For a comprehensive look at 25 different calendar systems (including Hebrew, Gregorian, Julian, Mayan and Hindu), and corresponding sample code in Lisp and Java, Reingold & Dershowitz’s Calendrical Calculations is an unparalleled resource.