Acid Media
Renders a scrollable list from HTML selects for easy data picking on touch devices. It comes with theming capability, optional jQuery Mobile integration and multiple display modes: Inline, Modal, Bubble, Docked Top & Bottom. It works with optgroups as well.
Apycom.com
jQuery Dropdown Menu with stunning visual effects and animations. Unlimited levels; Full cross-browser compatibility; Fully accessible even when javascript is turned off, as a pure css menu; Search engines optimized; Clear unordered list (LI and UL HTML tags) structure of jQuery menu; Easy to setup and update; Fantastic animation and transition effects; Multiple pre-desinded color schemes; Completely customizable styling with CSS; Extremely small - 3kb uncompressed.
harvest
Chosen is a JavaScript plugin that makes long, unwieldy select boxes much more user-friendly. It is currently available in both jQuery and Prototype flavors.
Fast, simple and light jQuery plugin to customize HTML selects
Per Vestman
Yet another jQuery plugin to style/replace select elements.
Willington Vega
Enhances standard form input fields helping users to select (or type) times.
jQuery mnmenu, simple dropdown menu
Marc Nuri
jQuery plugin to create dropdown menus from ul lists.
Ryan McGeary
jQuery plugin that turns select boxes into flex-matching incremental-finding controls.
Igor Vaynberg
Select2 is a jQuery based replacement for select boxes. It supports searching, remote data sets, and infinite scrolling of results.