No, this isn't a Web2.0 site, but man can not live by Web2.0 alone. The New York Times provides a page on their site that poses a question (usually relating to a news story) and then asks scholars and experts to comment creating a virtual debate. The comments are usually brief and insightful. This a great tool for studying current events with secondary students and showing them  the multiple perspectives that can be brought to a problem.

Recent topics include: single sex education, the flat tax, isolationism, population growth rates, and the American work ethic.

http://www.nytimes.com/roomfordebate