I use the screen protectors from the AT&T website. They fit perfect compared to a few of the third party brands I've used. The cheap ones always seem to have a problem laying down around the edges, especially around the bottom where the menu, home, back and search buttons are and they're touchy enough as it is. Dust tends to get under the edges and it looks terrible.
I don't have too much faith in the gorilla galss or whatever. I work on a drill crew and one of the guys has some pretty deep scratches on his Captivate and he keeps it in his pocket all day, screen-to-leg.
He had a little trouble working out the bubbles on the screen protector I gave him, due to the scratches.
"If you are flammable and have legs, you are never blocking a fire exit" ~Mitch Hedberg