The Android Device Manager might get the basics taken care of, but Cerberus goes a few steps farther. It's a powerful security suite with features like SIM locking, device alarms, remote lock, remote wipe, remote picture taking, and location tracking. It would usually cost you €2.99 (about $4) for a lifetime license, but it's free for the next day in celebration of the app's third birthday.
Cerberus has robust functionality on standard devices, but it can also take advantage of root access to move to the system partition so it persists between device resets. The new feature added in v2.5 is Radar Mode, and it's pretty ingenious. If you use GPS to track down your lost phone to, say, someplace inside a building, Radar Mode can get you the rest of the way there. It toggles the hotspot on for the lost device, then uses the signal strength to guide you in the right direction.
If you like free stuff, all you need to do is log in with a new account during the promotion. The upgrade happens automatically, but you have to take advantage of this deal today before 6AM GMT on April 26th – that's 11PM PDT on the 25th.
[+Cerberus – Thanks, Sruly]