Richard is right. The Zagg invisible shields are awesome!!! I used my first one on the Droid 1 and when I took it off before I sold it the screen looked like new. I have one on my Thunderbolt now and I would only recommend this brand.
On the Verizon one, there is constant oil marks all over it. What would be a good store to go to to buy a screen protector for cheap?
Buy from Amazon. One thing to be aware of though....if you use any glossy/crystal screen protector, they will show fingerprints like crazy. Steinheil makes a great anti-fingerprint screen protector that has a matte finish. Many people do not like matte screen protectors as the major complaint is that the matte finish will slightly dull the screen image (same as privacy screens on notebook computers). You can find screen protectors as cheap as $3 or $4 for a package of 3 on Amazon. Steinheils run around $11 to $14 for 2 on Amazon.