Author: Arie Molendijk.

This script allows us to (i) chain select boxes and to (ii) use javascript in the options. It even works for IE7/8.
The inbuilt select box arrow is replaced with a custom one.
The width of the select boxes does not exceed the width of the main option, leaving more space on the page. But long options are entirely visible when the main option is clicked on.

Explanations and demo HERE.