I'm using avast anti theft not sure if you need to be rooted or not as I am, you can even hide it so it doesn't show up in apps if your phone is stolen or lost and allows remote erase, lock, locate it's awesome
Samsung has a "Find My Phone" website to use after your phone is registered with them. I tried it and it's very accurate. I also have it through Lookout & Carbonite Mobile.
-Locate Phone
-Activate Siren
-Record Sounds
-Take picture with front or back camera
-have a notification sent to the phone and when the person dismisses it, take a photo with front camera
-Turn flash on
-Have texts/calls forwarded
-sim card swap notification
-change pin/password
-erase phone
These are really only the beginning. Off the top of my head. There are way more features and it's all free.
Only thing is there's only a website to do these things to your phone and the user interface is basic/ugly but it's worth it IMO.
Well, Android Device Manager, already builtin to your phone, is the least resource intensive of all if that matters to you.
Do you have Lookout pre-installed? I'm not sure if that is carrier dependent. If that's something you have to have on your phone anyway, then I would use that as a backup to ADM but if you don't have to have it, Lookout can be a drain under certain circumstances.
Android Lost which was previously mentioned has some good features but I personally am not comfortable with what it requires, so you will have to decide that for yourself. Many people do use it and are happy with it but for me it poses more of a risk than a reward.
Any of the antivirus apps have the feature so if you prefer one of them over Lookout you could use that.
Find My Mobile from Samsung recently had a security issue. I don't know if it has been fixed.