Easy configurable Ajax-enabled JavaScript combobox with autocomplete feature
BS Editor: Easy configurable DHTML JavaScript combo Box with Ajax support, AutoComplete functionality and wide cross-browser compatibility. Features include type-ahead, keyboard support and ability to display images in the dropdown list.

dhtmlxCombo can be easily converted from existing HTML SELECT or populated with JavaScript. The component works fast and smoothly with large sets of data, loading list of suggestions dynamically on demand.

dhtmlxCombo can be used in four modes:
editable select box - user can either select a value from the list or type a custom value;
read-only select box - user can select just one value from the list;
filter - all the data is loaded on the client-side and as user begins to type, the list is narrowed to the appropriate values basing on the first typed symbols;
autocomplete - the list is loaded and shown as user types in input box, autocomplete text appears basing on first typed symbols.

The component is distributed under both GNU GPL and commercial license. you can free download dhtmlxCombo 2.5 now.