Cascading select menus in Rails?

I'm looking for a canned solution to creating cascading
select menus in Rails. Kind of like optgroup, except that
the lower-level items live in their own menus, as seen in:

http://www.webdevelopersjournal.com/articles/cascading/cascade_explained1.html

Can anyone point me to some nicely packaged technology,
so I don't have to fight with the JavaScript myself?

-r