Improve Your Google Site Navigation
I had a teacher come to me yesterday wanting to rework her Google Site to have the navigation be clearer and easier to use. Collapsed headings is a great way to do that so all of the layers are hidden under the appropriate headers. Although not intuitive, Google does make it possible assuming you layer your pages under your homepage.
For a visual of how to set up your navigation to be automatically collapsed, here is a screencast to show you the process.