Lucid Chart is one that I often recommend. Until this week Google Apps Marketplace apps could only be added to a domain and a user's account by a domain administrator. That has changed with the latest update to Google Apps. Now Google Apps for Edu domain administrators have the option to allow individual users to add apps from the Google Apps Marketplace. Domain administrators can also choose to customize which apps are made available to their domains.
Applications for Education
In the past if there was a Google Apps Marketplace app like Lucid Chart that a teacher wanted to use, he or she would have to ask a domain administrator to add it. This update makes it possible for domain administrators to give teachers the rights to adding the Marketplace apps that they want to use.