Flexselect – Incremental finding control for select box using jQuery. Flexselect is a jQuery plugin that turns select boxes into flex-matching incremental-finding controls. Think of it as Quicksilver squished into a select box.
Ajax Combobox – A jQuery plugin for creating a text box it can autocomplete and pulldown-select.
HeapBox – A customizable replacement for HTML select using jQuery. This jQuery plugins has features like event handling, callbacks, themes and much more.
SelectBoxIt – SelectBoxIt is a jQuery selectbox plugin for mobile, tablet and desktop.
ddSlick – A free light weight jQuery plugin that allows you to create a custom drop down with images and description.
DropKick.js – Beautiful custom dropdown select boxes with jQuery. A jQuery plugin for creating beautiful, graceful, and painless custom dropdowns.
Select2 – A jQuery Based Replacement For Select Boxes. It supports searching, remote data sets, and infinite scrolling of results.
Chosen – Chosen is a library for making long, unwieldy select boxes more friendly. A jQuery plugin for a user friendly select box with advanced supports and features.