Windows only: If you use Windows Media Center to manage your movies, TV shows and music, then you need to grab Media Browser, an open-source plug-in that displays your downloaded media and all its associated metadata and artwork in one slick layout.
After installing the free, open-source Media Browser plug-in, it only takes a few minutes to zip through the one-time setup wizard and choose which media you'd like the tool to aggregate for you. Then fire up Windows Media centre, and the Media Browser option will be listed among the centre's native Movie, TV and Music choices.
There are plenty of other Media centre plugins to choose from, and a couple of weeks back we highlighted the similar My Movies 3, but this one gets high marks for the way it aggregates a wide range of recorded or ripped media and presents it with just enough eye-candy to make it pretty without being cluttered. It's also open source, and with its low price of free, very easy on the wallet.
Media Browser only works on Windows Vista and Windows 7. What kinds of plug-ins improve your Windows Media centre experience? Kick around your ideas in the comments.