I am one of the co-founders of Koofers.com (one of the LaunchBox08 portfolio companies) and we have a VERY in depth professor rating system.

Check out our page and video over at CrunchBase for more info: http://www.crunchbase.com/company/koofers-com

Feel free to E-mail me at michael@koofers.com with any of your thoughts, comments, or suggestions.