Something you could try, though not very often on the same disc, is Brasso. Dab a little bit on a clean, preferably smooth, cloth and very lighty wipe it over the scratches. Take care to keep the Brasso as close to the scratched area as you can, as this process removes a light layer of plastic. Let the disc sit for at least 15 minutes so the polish can dry. After the 15 minutes, take a clean part of the cloth (or a different cloth entirely) and VERY gently, from the inside out and with a slight pressure, wipe the Brasso off. Make sure to get all the polish off. Try the disc. You can do this again if it doesn't work. But since it removes a very light layer of the disc, you shouldn't do it more than two or three times. It's been a while since I've done it, but as I recall, it's worked on every disc I've tried it on.
This is exactly why I love blu-ray so much. Much harder to scratch.
I tried that Brasso on a dvd and it just scratched it up even more.
Just be careful if you use it and don't overuse it like I did.