I bought a new lens for my Gameboy Advance. I didn't even know it was separate from the screen until I went looking on Ebay for a new battery cover and saw that you could buy a battery cover, a lens, and a screen protector for around $10. It looks amazing now! My old one was all scratched and covered with this scratch repair coating for eyeglasses. I was stunned to see how clear everything looks through the new lens. It might even look better than new, since the one I got is glass and the original was plastic.
The battery cover isn't an exact color match though, and they sent 2 and one broke after I removed it twice, but oh well. I'm too ecstatic about being able to actually see what's going on to care about a battery cover.