MobileDefense.com --It's in closed beta just now but a great app that takes up a small footprint and uses very little battery power. Enables precise locating and alerting of phone, remote lock/unlock, and eventually, remote backup and wipeout.
I am currently using Mobile Defense. Has web interface and also the app is hidden. Once installed on your device it cannot be reopened from the device which i think is awesome so someone can't just uninstall it.
I have used Smrtguard, but could not find a way to make it hidden so that it couldn't be uninstalled if stolen (and they knew what they were looking for). It was password protected on my Storm 2 so no one could uninstall or access it but couldn't find that option in the android version.