Smart Flex Comboboxes is a Flex widget for making multiple level choices. It allows the user to have several levels of choices where a choice at an earlier level can change the values displayed for the choices at the next level. You can also have disabled items. Selection can be done using the mouse or the keyboard.
PHP Autocomplete is an auto-complete and combo box component for PHP developers. A working auto-complete text box requires only two lines of PHP code. It features support for multiple dependent, cascading, nested drop-downs, customization with templates and images, the ability to quickly set up fields for tagging, built-in combo box support, and loading of remote data with built-in AJAX/JSONP support.