Honestly you dont need one. The phone has gorilla glass. We have a demo vibrant at my store (radioshack), and we've tested that screen, including stabbing as hard as we could with a screw driver, its still flawless. If something hits it hard enough to actually damage the screen its gonna go right through a screen protector.
Zagg shields are amazing too: ZAGG | invisibleSHIELD | Samsung Vibrant Galaxy S T959 Cases, Screen Protectors, Covers, Shields, Skins, Invisible Shield
It's what I use.