FullCalendar is a jQuery plugin that provides a full-sized, drag & drop event calendar like the one below. It uses AJAX to fetch events on-the-fly and is easily configured to use your own feed format. It is visually customizable with a rich API.

Draggable Events

March Invoices
Call Emy
Dinner with Team
Meeting with Support Team
Meeting with Sales Team
Design an iOS App
Company Party