A CyanogenMod team member has been building an open source security app, and it has been released today. Unlike the many other options out there, this one is simple and beautiful. Basically, you set a trigger for the device, and when you text it that trigger, it will react according to your settings. It can sound an alarm, locate your device (text you back an address), lock your device, and even wipe it entirely. All from one text (which you should definitely make unpredictable).
When you install this app, everything is disabled so you can customize it all first. It’s all free and open source too, so it’ll cost you nothing to get some extra security. Unfortunately, this app is US only right now, because of the way it finds the phones location. So if you are a US resident and running ICS or newer, go grab it!