Unfortunately, the 360 is notorious for beating up on discs. If you play a game hard (like I do with madden) you should always consider installing the game and running off the HD. The disc has to be in to play but its not constantly moving.
Now with a scratched disc, before you go out and spend any money you can try a gamer home remedy by scrubbing an abrasive toothpaste (like something with baking soda in it) all over your disc with your fingers or a cloth. Sounds barbaric I know but it works if the scratches aren't too deep.