This page has a double drop-down menu at the head. It can be very useful
for sites with many pages and can quite neatly replace several single drop-down menus.
You can select a subject in the left-hand menu and then choose a page-to-go in the right hand menu. Of course, the right-hand menu updates according to the subject you have chosen.
The triple menu for freeing the mind has lots and lots of files, so its code appears to be complex, when really it is quite simple.
Go here for the code.
There is also another page on drop-down menus using different code.