I bought some Pelican brand screen protectors for the PSP which happen to fit perfectly vertically, and with .25 inches removed horizontally work very well. They are about $9.00 (a little pricey), but are made of thicker plastic than normal so they are MUCH easier to pull off and reposition as well as avoiding/removing bubbles. Just make sure you trim off a quarter inch of width and notch a corner so you can get it back off. It's no fun trying to scrape it off without an exposed corner.

Larry