Chosen
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.
Tagged: multiselect
Select2
Select2 is a jQuery based replacement for select boxes. It supports searching, remote data sets, and infinite scrolling of results.
MagicSuggest
MagicSuggest is a multiple selection auto suggest combo box for Bootstrap 3.
multiselect
This is a user-friendlier drop-in replacement for the standard with multiple attribute activated.
Simple Combobox
A combobox plugin
Listbox.js
Listbox.js is a simple jQuery plugin that provides a more powerful alternative to the standard `select` tag
jQuery easySelect
A plugin to present multiple select elements in easier way.
Shuttle
A jQuery plugin that is a shuttle box ui.
jQuery Touch Multiselect
jQuery plugin to have a touch-fitted multi select input field..
jQuery dropList
dropList is a lightweight jQuery plugin to custom UI style for drop down list. The plugin has droplist, multilist and combo list (search and dropdown) options