Excellent JQuery Treeview plugin

Dynatree is a dynamic JavaScript tree view control with support for checkboxes, drag'n'drop, and lazy loading. I have used in a project and it is quite simple to use.
Main features:

• Open source (MIT and GPL License)
  
• Optimized for large dynamic trees (DOM elements are only created when really needed).
• Programmable through a rich object oriented interface.
• Support for lazy loading and Ajax.
• Checkboxes and hierarchical selection.
• Supports drag and drop.
• Support for persistence.
• Keyboard aware.
• Initializes from HTML code, JSON, or JavaScript objects.
• Implemented as a jQuery plugin.

Quick sample:
http://wwwendt.de/tech/dynatree/index.html