I bet you have them - CDs, DVDs or video game discs that don't work quite as well as they used to. A skip here, a jump there, a great big freeze up. I have a couple of solutions. None are free (though two are pretty darn cheap), but they are a lot less expensive than wasting your digital media.
First, I have heard interesting things about putting a coat of Rain X on a disc to improve the reading. The concept makes sense - the Rain X fills in microscopic imperfections in the surface of the disc, allowing the laser to see through to the content layer. Actually, a little Rain X might work as a preventative tool, protecting the disc from minor damage by coating the surface.
Second, you might try the toothpaste method:
If neither of those methods are working for you, or you know that you are dealing with more serious damage, you might want to try the magic product :
I bought one of these (the classic version) on a crazy whim about five years back. We had four little kids, and our DVDs were always being mistreated. It was so frustrating to own movies but not be able to watch them, or to have to press the forward button to skip over the damaged parts. There is only so much that regular cleaning can do, especially if you aren't taking proper care of your things in the first place. (Guilty.)
With this contraption, you spray the surface of the disc with a resurfacing fluid, then use the machine to buff out the top surface of the disc. You are basically wet sanding it very finely. There is also an included felt pad to polish it after the sanding.
I have done approximately 50 discs with mine, and I still have plenty of solution and I am still getting good results. I think I have only had one disc that was unrepairable (and I'm not surprised - there is only so much magic one can do.) It has definitely been a worthwhile investment