One of the most popular applications of AJAX - The autocomplete

The autocomplete is certainly one of the most seen and used AJAX scripts, however, there are still a few twists and tricks that may be used to spice usability and appearance. Have a look at the following great scripts:

Search Autocomplete - .NET	Yet another AutoComplete
Autocomplete - jQuery	dhtmlxCombo + Autocomplete
AutoComplete - JQuery	AutoSuggest