While there is no shortage of security apps on the Play Store, aeGis one stands out a bit for a few reasons. For starters, it's dead simple to use. Set up a specific trigger phrase and you can text your phone to lock the display, remotely wipe, find the address of, or sound an alarm from your phone. There's no web interface, unfortunately, but this app trades the elaborate suite of services of something like Avast for simplicity.
What's even cooler is this app is entirely open source. Built by a member of the CyanogenMod team as a side project, the entire codebase is available on Github here.