Curt Clifton has a nice script to do the search for projects with no Next Actions, called
Verify Next Actions, which actually goes through and adds a prefix to the names of projects and action groups that don't have any available Next Actions. You can also use the Stalled projects selector in the sidebar to get a view of projects (but not action groups) that don't have any Next Actions at the moment, although this will show you projects which have future Next Actions as well.