The screen protectors I'm using on my 770 and N800 are
cell-phone/smartphone protectors which happen to be big
enough for the tablet screens.
They give the screen surface a bit of a leather-like texture
which is good for using it with fingers. You leave absolutely no traces.
The stylus scratches the surface a bit, but that's negligible.

All in all I'm happy with the protectors. The one on my 770
has been there for about a year and still no signs of wearing off.
I don't remember the brand and they were actually rather cheap.