At.js is an autocompletion library to autocomplete mentions, smileys etc. just like on Github.
Tag-it is a jQuery UI plugin to handle multi-tag fields as well as tag suggestions/autocomplete.
Flexdatalist is jQuery autocomplete plugin with support for
<datalist>. There are many options, methods and events to customize plugin.
jQuery.textcomplete is a jQuery plugin that introduces autocompleting power to textareas, like a GitHub comment form has.
Horsey is a progressive and customizable autocomplete component. It supports every sane browser and IE7+.
Awesomplete is an ultra lightweight, customizable, simple autocomplete widget with zero dependencies, built with modern standards for modern browsers.
jQuery Autocomplete plugin is a lightweight simple and easy in settings autocomplete like Google.
Autocomplete.js is jQuery plugin that improve your search with hints. Autocomplete.js also has some options to customize.
It gives a search preview from Json object(s) via same domain Ajax request or cross domain jsonp and offers data compression inside Local Storage.
Autocomplete Table is a jQuery plugin that provides suggestions from a multi-column table in a dropdown list while the visitors type into the input field.
Flexselect is a jQuery plugin that turns regular select boxes into Quicksilver-like, flex-matching, incremental-finding controls.
Autocompleter is a simple, easy, customisable autocomplete plugin with cache support (one more alternative).
Marco Polo is a jQuery autocomplete plugin for the discerning developer.