FORM dropdown Feild with Search Option

Hi,
I am creating a form, it is rather complex form, and has numerous dropdown, radio buttons and text boxes. One of the dropdown will have allot of options to choose form, ie numerous departments.
I would like to ask is it possible to create such dropdown and provide ability to the user to search through the dropdown list and select the desired department.
I am open to suggestions or just code implementation to make it happen.