Microsoft's SmartGlass is a product that will probably become a staple of platforms, especially game consoles, as we move forward. The idea is partially for your mobile device to be something of a remote control for your system, but it goes well beyond that. And, to make things better, Microsoft isn't keeping it proprietary, and has just released the Xbox SmartGlass app for Android devices.
On the basic level, the SmartGlass app will let you control media playback on your Xbox via your Android device. It will also let you navigate the Xbox dashboard, search for content, browse the Internet, track achievements, and message Xbox friends. That alone would be pretty solid functionality, but in the future, there are plans which will allow SmartGlass to bring more interactive functionality to your mobile device like second-screen gameplay, and getting more info about the actors in the scene of whatever movie you are watching. In this respect, it sounds something like the Wii U tablet controller, except that any Windows 8, Windows Phone 8, or Android device will be able to be used.
Well, not every Android device. The app requires Android 4.0 or higher, so you'll need to be at least on Ice Cream Sandwich to get the goods, and it isn't currently available for Android tablets. It seems likely that will change over time though.
So, if you're an Xbox 360 user, you'll definitely want to give this a shot. The Xbox SmartGlass app is available for free in the Google Play Store