Any 3/$5 plastic protectors will work. When one gets scratched up (and I've uses one for a few years without having to use the second one), replace it.
As far as cases, after accidentally flinging my phone against a wall at a pretty high speed, I won't buy a phone for which there isn't an Otterbox Defender. It didn't even scuff the wall. (And the next day It fell off the desk, face down, on a hardwood floor. Bad couple of days. No problem, though, except for picking a little cat hair off the case the second time.) Until they make one out or transparent armor plate, that's the case I'll be buying.