On this days it is so easy to find a Javascript Datepicker on the field but if you really want a Datepicker with lots of feature you should definitely check out the jQuery UI Datepicker. This jQuery plugin is very configurable to fit your needs. In the following list you can find some of its features.
In order to use this jQuery Datepicker you only have to point to the correct elements with a CSS3 selector, for example if I have a input with id = datepicker then to attached the jQuery Datepicker to that element I would use the following code.