Tigra Calendar is a sharp, easy to install, FREE JavaScript calendar. It works great on all browsers. Only criticism is that it doesn't force any formatting (e.g. 01/01/2008) if the user enters the date in manually. It also starts at today's date, so if you implement two boxes, and want the second box to come up as the first date (e.g. like check-in and check-out for travel site), you have some work to do. But, can't fault that. Great support, documentation and forum, esp for a free app!