As Brad Frost points out in his responsive navigation patterns article, small screens make designing a usable menu difficult.
For a large site with lots of menu items (e.g. a resource site) how do we cram it all into a usable menu with a good mobile UX?
It’s tempting to just take the “easy route” to mobile menus and use native select (dropdown) menus. While it’s snappy and usable, it’s a little disorienting as it removes the user from the look and feel of your website.
I came across this drill down menu from 2009 and think it might work well on a small screen. I haven’t tried it out yet, but nothing else looks promising at the moment.