Cerberus can be activated by both it's web service and via text message. If you're rooted, it can be integrated into the system apps and so survive a complete wipe. FYI, NO app will let you track your phone while it's turned off :)
It can also turn on the GPS remotely, has real time tracking using Google maps (looks like Google navigation in a web browser), take pics/record sound & video, sound an alarm, hide itself from the app drawer so thieves won't know it's there, remotely lock the phone with a code, wipe the system, display messages, download the last 10 texts and phone calls, and LOTS more.
Cerberus is $5, and worth every penny.