JqxComboBox

The jqxComboBox control contains a list of selectable items displayed in a drop-down. Users can enter information in the text box portion and search for a specific item. The widget comes with built-in auto-complete support. It performs exceptionally well with thousands of items and supports keyboard navigation and rich list items visualization.

Complete documentation is here.

jqWidgets is a commercial product, which depending on how you use it, requires a license fee. Complete details are on jqWidget's website. The product is well supported.