Is there a microformat for menu (nav)?
I didn't find one here: http://microformats.org/wiki/Main_Page
There is no specific microformat for menu/nav, but the XOXO (Open XHTML Outlines) specification provides an open outline format that can be used for lists that conform to the HTML list module. XOXO is incredibly easy to implement; I've been using it as a default class for certain lists for a long time now. More/references listed below: