Does anyone know of a good screen protector that does not mark or scratch.

Zagg

Use this on my Edge 800. very tough.

I just use cheap glossy protectors and replace them when they get badly scratched, as that’s rather the point. Glass can scratch, my 3G has scratches on it from hard metal objects so just get a packet of gloss protectors and replace them when they get shabby. I fitted one to my iP4 when I got it new, and finally replaced it last month. It looked like a brand new phone.
I also have a rear protector, and a Belkin clear case that Apple gave away free, and that’s really knocked about, but the phone’s pristine nearly two years on.