Find Your Lost Smartphone with Google's Upcoming Android Device Manager
If you ended up dropping your phone between those couch cushions, Android Device Manager lets you quickly ring your phone at maximum volume so you can find it, even if it's been silenced. And in the event that your phone or tablet is out of earshot (say, at that restaurant you left it at last night), you can locate it on a map in real time. If your phone can’t be recovered, or has been stolen, you can quickly and securely erase all of the data on your device.
This service will be available later this month on devices running Android 2.2 or above; to use it, you also will need to be signed into your Google Account. There will also be an Android app to allow you to easily find and manage your devices, but details on that have yet to be made public. So, don't lose your phone in the meantime!