AjaxLine

ExtJS TreePanels

ExtJS has its own implementation of tree widget - TreePanels. It's on of the best tree controls. Has lots of features including drag and drop. Has powerful api and good docs. For commercial projects requires license.

QooXdoo Tree Widget

The tree package contains classes that allow you to build up visual trees, like the ones you are familiar with e.g. for browsing your file system. Expanding and collapsing tree nodes is handled automatically by showing or hiding the contained subtree structure. Good OOP code base.

jsTree

jsTree is a javascript based, cross browser tree component. It uses jQuery and Sarissa (optionally). jsTree has features like ExtJS. But codebase less clean (it's writen way which is far from OOP).

TreeView

Leightweight and flexible transformation of an unordered list into an expandable and collapsable tree, great for unobtrusive navigation enhancements. Supports both location and cookie based persistence. Codebase very simple so this tree is good component for customize and integration to project.

Destroydrop

dTree is a free JavaScript tree menu. dTree is very simple to set up and use. You don't have to worry about adding pages to the tree in a specific order, which makes it ideal for generating a tree from a database.

jQuery File Tree

jQuery File Tree is a configurable, AJAX file browser plugin for jQuery. You can create a customized, fully-interactive file tree with as little as one line of JavaScript code. Currently, server-side connector scripts are available for PHP, ASP, ASP.NET, JSP, and Lasso. If you’re a developer, you can easily make your own connector to work with your language of choice. It has little JavaScript code but html generation on sever side code (it generates html for nodes - jsTree and ExtJS tree for example uses json or xml to get new nodes).

jQuery Simple Tree

jQuery SimpleTree Drag&Drop plugin is intended for displaying tree structures. Simple and good looking but with lots of hardcode in it so it will be hard to customize it.

DHTML TreeView

One more lightweight JavaScript tree.

Graphic JavaScript Tree with Layout

A JavaScript Tree component which implements the J.Q.Walker II layout algorithm.

Summary

One of the best ways is to create your own tree based on simple ul, li markup or choose some simple TreeView. But in some advanced cases when you need to edit nodes on fly, do drag and drop, change themes the best solution will be ExtJS Tree.