Gridster is a jQuery plugin that allows building intuitive draggable layouts from elements spanning multiple columns. You can even dynamically add and remove elements from the grid. It is on par with sliced bread, or possibly better.
Cyclotron is a simple jQuery plugin for dragging 360° panoramas (cylindrical projection) and other seamlessly looping images around.
HTML5 Sortable is a jQuery plugin to create sortable lists and grids using native HTML5 drag and drop API.
Nestable is an interactive hierarchical list. You can drag & drop to rearrange the order. It even works well on touch-screens.
Overscroll is a jQuery plug-in that mimics the iphone/ipad scrolling experience in a browser. The plug-in adds a draggable drift to overflowed DOM elements as well as a set of fading 'thumbs'. OverScroll runs best on Safari 5+, Chrome 5+, and Firefox 3+ but should run just fine on most modern browsers.
TableDnD is a jQuery plugin that simply adds drag & drop functionality to tables.
This TableDnD plugin allows the user to reorder rows within a table, for example if they represent an ordered list . Individual rows can be marked as non-draggable and/or non-droppable. Rows can have as many cells as necessary and the cells can contain form elements.
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)