This started out as an extra function for Ext.form.ComboBox, and Jeff pointed out that you couldn't use the keyboard to navigate.

I've added basic searching to and extended Ext.form.ComboBox to create Ext.form.SelectBox. Type a letter to jump to and select the first matching result. Press that same key to find the next match. Home/End jump to the top/bottom of the list, PgUp/PgDn move the selection one 'page' at a time. There's only one new config option, searchResetDelay which is the amount of time before a search is reset. With a little extra effort this could be modified to support a deeper search so that typing 'Ver' fast would match Vermont instead of searching for matches to V, E and then R.

See the example page for more details:

May 29, 2007 - Fixed a bug with the way superclass functions were called that broke when using an Ext.form.Form

Edit: I didn't test it in Safari, fixed a few bugs there and with page up/down scrolling the page.