The Columbia Schools of Journalism already keeps a listing of print and broadcast media, and its ownership status. Expand this to include Internet sources, and allow users to track and record their 'consumption habits.' Users can then see if 80% of their news and information is coming from the same parent company, what percentage of their information comes from big media companies and how much is smaller-scale or independent journalism/media.
Using existing data from broadcasters, users can select the programs they watch (NBC Nightly News, NPR Fresh Air, Bill O'Reilly, Democracy Now, Daily Show) and read (Drudge Report, The Daily Beast, Financial Times, Washington Post), and be provided with a pie charts and graphs illustrating the ownership and diversity of the sources that inform their opinions.
This would be a pretty simple idea to execute, and might be done by simply working with Columbia to expand their current project. It would be ideal to host it on an expanded Fed, State and Local OpenCongress-style Sunlight Foundation page, where users can come to learn about and influence their government. An extremely cheap and easily developed tool, with great benefits.