For a better listing see this post: 10+ JQUERY SELECTBOX/DROP-DOWN PLUGINS
1. oCombo – Image Integrated Selectbox
A jQuery plugin that convert your selectboxes into an imposing components. If you require images for your selectbox items, oCombo is a perfect solution for your site.It provides simple and flexible way of changing your selectboxes into a image-integrated selectboxes.
2. jQuery Two Sided Multi Selector
3. jQuery checkbox
Lightweight custom styled checkbox implementaion for jQuery 1.2.x and 1.3.x.
4. Simple chained combobox plugin for jQuery
Very simple chained selects plugin for jQuery with JSON processing and callback feature, chain multiple selects with ease.
5. asmSelect jQuery Plugin
A progressive enhancement is applied to the select multiple that makes it much easier to use. This enhancement automatically hides the original select multiple, and instead presents a regular select showing the available options, and an HTML list showing the already-selected options.
6. jQuery UI MultiSelect Widget
This is the successor and port of jQuery MultiSelect Plugin to a jQuery UI widget. While both will actively be maintained, it is recommended you use this version over the plugin version.
7. jQuery Custom Select Box
Create nice select boxes.
8. Auto-Populate Multiple Select Boxes
Allow the user to select multiple select boxes and to automatically populate the sub-category.
9. Select Box Manipulation
A suite of plugins for working with drop down lists.
10. Choose Plugin (Select Replacement)
This plugin allow to select data with ID|LABEL format like an xHTML SELECT. Selectable data is loaded by Ajax. It provide mechanism to auto fill multiple data fields.