FullCalendar is a jQuery plugin that provides full-sized, drag and drop capable calendar. It utilizes Ajax to fetch events on the fly. It is easily configurable to use custom feed format and also has an extension for Google Calendar. The calendar is highly customizable and has support for user event triggering for window resize, loading, day click, event click, event drop, etc.
FullCalendar - jQuery Calendar Plugin with Drag'n Drop and Ajax Capabilities