I got the ones that Apple sold at their store. Not sure what the brand is, but they're awesome.
They work by static cling, and stick amazingly well to the screen, but also let you peel them off easily enough to clean the screen if you need to. I pulled it off after a day in my pocket, and the actual screen was completely unblemished. They rock SO hard.
I had 'em on my SLVR. This product is pretty solid. Some work to get it on but check out the amount of protection you're getting in their video demo. http://www.shieldzone.com/iphone-screen-protector
Actually I got one of the iCrytal protectors Apple is selling in their stores. Works fantastic and number easier to put on than any other product I've tried (include invisibleshield and bestskinsever). I highly recommend it.