Go to http://www.expedia.com, click on flights at the top, & then make sure you're on the 'Roundtrip search' page. Next to 'Departing', click the calendar. It's an excellent piece of work.

Here are some others that are close, but not exactly what they have at Expedia:

http://developer.iplanet.com/viewsource/husted_calendar/husted_calendar.html <-- My fave so far

http://www.irt.org/articles/js068/index.htm <-- Scroll to the bottom to click on the example

http://irt.org/articles/js001/index.htm <-- It's a start, but it doesn't go far enough

http://wsabstract.com/script/cutindex1.shtml <-- Nothing here specifically addresses my issue, but there are some cool calendar/clock scripts nonetheless