DHTML Widgets

Lightview
Content overlay (modal dialog). This is the best one I have found. Must be licenced.
 * light view

DHTMLX Combobox
Handy little tool to create combo boxes.
 * Combo Box
 * I now prefer jQuery Autocomplete Plugin

Scriptaculous
Visual effects.
 * website

TinyMCE
Rich Text editor
 * Using Tiny MCE
 * website

jQuery Autocomplete Plugin
Very good combo box. bassistance.de