Here's a thread with a lot of advice:
http://club.myce.com/f3/scratched-cds-help-74406/I've used devices like SkipDr to polish discs with just mild success. It's really for vvery superficial scratches.
Try different drives if you can, some drives will read more successfully.
Try EAC / Exact Audio Copy, but you might check the other thread read up on it for more advice. I used it years ago.. it might just make the copy take forever doing error recover and wear and tear on your drive as someone seemed to comment in the other thread (but then the OP used it and was happy)
I have used silver polish (wish is very mild) and Brasso with some success. Also if any scratches have left a bit of plastic go up from the surface of the disc, a gentle fingernail can sometimes improve the condition.
when all else fails, I coat the disc with OIL! It is tricky.. you need to polish it so it's optically evenly coated, and thin coat, but you want it to "fill in" the scratches somewhat too. Sometimes it has worked miracles, other times I can't get it right and it's just worse.
