Today Google officially released the "Android Device Manager" - a locating device directly built into android devices.
Equivalent to the "find my iPhone" feature for Apple, Android users can now locate and ring phones and tablets remotely. Simply go onto the web and ring the phone - it will override any silence/vibrate features that you have set on on your phone. Additionally, it will display your phones location on a map using its GPS coordinates.
You can also enable it to do a "wipe" of information in the case of a theft, but you have to make sure you add this functionality to your phone with it in hand before you can activate this remotely.