JavaScript Library for Enhancing HTML Select Boxes: Chosen

Chosen is a tiny JavaScript library for enhancing HTML select boxes. This plugin hides standard HTML selects and provides an alternative using modern HTML and CSS. That means it’s possible to add behaviour that standard selects don’t support without losing support when JavaScript is turned off.

Instead of forcing your users to scroll through a giant list of items, they can just start typing the name of the item they were looking for. Non-matching entries are removed from view and choices can be selected using enter or mouse click.

It is currently available in both jQuery and Prototype flavors.