Here’s a little something I put together earlier- tree/branch style navigation, powered entirely by CSS3 selectors, using valid XHTML 1.1 Strict code.
It seems to work in every browser, though IE7 doesn’t seem to support the coolest feature- the ability to have the page keep branches open while you navigate through branches higher up the tree. Not entirely sure what causes the borkage of course, but hey- IE’s Trident engine has never been one to play nice :-P

One Comment
Is nice =)
In case I click branch 2 without having clicked branch 1, it closes again. So might have something like: “in case someone clicks branch x, it automatically marks all lower branches as clicked too”.
Same with de-click in the other direction.