Minical is teeny (~300 lines of Coffeescript), and has no dependencies other than jQuery, its icon PNG and stylesheet (which has SASS variables for easy customization).
It has full keyboard support and also defaults to make the associated input read-only, so its value can only be changed by the date format specified in the plugin, alleviating unexpected JavaScript date-parsing drama. (It also works great on mobile, with just enough touch event handling to behave properly.)
