Ok, my MW2 game disc was cracked pretty bad, and it wouldn't read at all. So, what I did was:
I took some VERY clear scotch tape (This stuff: Scotch Tape!) and taped the top of the disc along the crack. Don't take the disc on the side that goes down! You tape the side that has the graphic on it. Then I pressed the tape down with gentle force, and popped it into my Xbox 360. It then read! If you do this, I would recommend installing it to your hard drive afterwords just in case. Here's a short guide for people who don't want to read all of this.
1) Get some clear scotch tape
2) Tape the cracked part of the disc on the 'upside' (Where the graphic is)
3) Press the tape down with gentle force
4) Put the disc in the console
5) Install to hard drive or play the game!
THIS CAN WORK ON PS3 AND XBOX 360! NOT SURE ABOUT WII.