This is sort of a follow up to a post about the Firefox addon Certificate Patrol.  The addon Perspectives also helps watch out for certificate related problems.  When you go to a secure web site, Perspectives can (with a click or automatically) check with several “notaries” scattered around the world and tell you whether they are getting the same certificate from that site as you are.  Read for more details.  Here is a link to the Firefox addon:  There is also an Alpha, very experimental Chrome addon

This project is out of Carnegie Mellon University  The notary server is open source, so anyone can run their own servers.  By default, the plugin uses several servers that seem to be run by the Massachusetts Institute of Technology.