One of the great things added to the Xbox Live is the Marketplace.  All Xbox 360 users with either a free Silver account or a paid Gold account can access Xbox Live Marketplace on their 360 from the Xbox Live blade.  Marketplace allows you to get demos, trailers, movies, TV shows, gamer pictures, themes and in game content like new maps, levels and player skins.  Often I'll check out if there are new game demos or trailers.  I like to try before I buy and playing demos is a great way to make sure you like a game before you buy it.  I'm a big fan of watching 720p movie trailers on my TV and will keep them around to watch again.  I don't watch the TV shows they offer but I do rent movies from XBLM.  The service has a vast collection of HD movies and is now the second most used content download service behind iTunes.