Prassu, I'm glad you asked this question.
I've been searching for a good app, too. So far, I've looked at Lookout, Prey, SeekDroid, and Snuko. I see shortcomings in all of them.
If GPS isn't turned on, the locate feature is very inaccurate.
If data isn't turned on, the web site won't be able to send the stolen notification to the phone. (Prey sends a text message, but I haven't been able to make it work on my phone - LG Ally).
Most of these apps can be uninstalled without a password.
Some display on the apps menu, which I would think is the first place a thief would look to try to disarm whatever is running.
So....what's the community wisdom on all this? Do I just have to hope that the thief doesn't figure out how to disable the lost/stolen app?