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.
typeahead.js is a fast and fully-featured autocomplete library that is inspired by Twitter's autocomplete search functionality.
Ajax Autocomplete for jQuery allows you to easily create autocomplete/autosuggest boxes for text input fields.
Built with focus on performance - results for every query are cached and pulled from local cache for the same repeating query. If there are no results for particular query it stops sending requests to the server for other queries with the same root.
Inputosaurus Text is a jQuery plugin that allows for multiple delimited values, parse hooks, autocomplete, keyboard shortcuts etc.
The jQuery Tagit plugin transforms an html unordered list into a unique tagging plugin. Why unique? Because jQuery Tagit uses jQuery Ui's auto-complete plugin to supply suggestions to users as they type.
Tokeninput is a jQuery plugin which allows your users to select multiple items from a predefined list, using autocompletion as they type to find each item. You may have seen a similar type of text entry when filling in the recipients field sending messages on facebook.
Address Picker Plugin is autocomplete filled by google map geocoder suggestions. Also map displays selected address, even while you navigate in autocomplete suggestions. Lat and Lng fields are just for information. You can even adjust marker position on the map
doubleSuggest plugin will set up a UI that suggest results as you type.
It will display two types of suggestions, first (and faster) the local data and second (and slower) the results from an ajax search query.