I have posted before the Media center plug-ins that I have used with my media center. After upgrading my Mediacenter PC to Windows 7, some of my favorite ones no longer work.
My absolute favorite : Web Guide (WebGuide) will not work with 7. I hope they come up with some type of fix / new version
However, there are a few great plug-ins that you should look at for media center 7.
Hack7mc has a great list that I think covers almost all of them. The only item I think they missed was MyMovies.
So head on over and check out the list. You should add this to your MC7:
http://www.hack7mc.com/2009/04/5-plug-ins-every-windows-7-media-center-install-should-be-using.html