Windows 7 already promises some great
content aggregation services for Media Center, but
SecondRun.tv addresses Media Center's biggest content gap today: Hulu.com.
Through the new app (now in beta), users can easily navigate free TV content couchside via a Media Center remote.
I personally have been using Gyration's excellent Air Music remote to toggle back and forth between Media Center and Hulu, but SecondRun will make life a lot easier.

Learn more about Media Center at Media Center University, exclusively at the
Electronic House Expo, March 11-14, 2009 in Orlando, Fla. Check out the complete
MCU agenda here. Media Center University is sponsored by the
Media Center Integrator Alliance (MCIA).
The elegant (so it seems) user interface lets you navigate through shows from the major stations very simply -- a heck of a lot easier than you can do today via Hulu.com.
Many integrators are ambivalent (to say the least) about Media Center, but at least you know there are thousands of third-party developers out there creating new applications for the platform. That's hard to compete with.
Media Center shows tremendous promise in the area of content aggregation, giving users the choice to watch or buy TV shows and movies from virtually any source.
More information on SecondRun and updates are available at
The Green Button forums.