FullCalendar is a jQuery plugin that provides a full-sized, drag & drop calendar like the one below. It uses AJAX to fetch events on-the-fly for each month and is easily configured to use your own feed format (an extension is provided for Google Calendar). It is visually customizable and exposes hooks for user-triggered events (like clicking or dragging an event). It is open source licensed under an MIT license.
NEW POST (2/3/14): FullCalendar 2.0 and how you can help
- Larger version of the same calendar
- "Basic" version of Week and Day view
- Google Calendar of US Holidays
- Fetching JSON events from a script
- jQuery UI themed calendar
- Selecting time ranges for creating an event
- Dragging external events onto the calendar
DISCLAIMER: FullCalendar is great for displaying events, but it isn't a complete solution for event content-management. Beyond dragging an event to a different time/day, you cannot change an event's name or other associated data. It is up to you to add this functionality through FullCalendar's event hooks.