SelectListActions is a jQuery plugin that allows you to perform several actions with HTML Select lists.
ajaxComboBox is a jQuery plugin for creating a text box it can "autocomplete" and "pulldown select".
SelectBoxIt allows you to replace ugly and hard to use HTML select boxes with gorgeous and feature rich drop downs. Twitter Bootstrap, jQueryUI and jQuery Mobile themes are supported right out of the box.
SelectBoxIt also provides first-class support for mobile, tablet, and desktop browsers, triggering the native "wheel" interface for mobile and tablet devices.