One of the most common problems people have with their cats is that they tend to scratch things we don't want them to: furniture, curtains, rugs, wood trim in the house, etc.  Some people immediately turn to declawing, but I think that's a pretty cruel practice, and advocate training and other alternatives.  Here are a few ways you can minimize scratching as much as possible.

1. Find a dedicated scratcher your cat likes.  I often hear people say, "But my cat won't use the scratching post!"  Maybe you need to try a different kind.  Some cats like the typical carpeted scratching posts and houses, while others prefer those wound with rope.  There are also bare wood and cardboard scratchers.  Cat nip can also be rubbed into a scratcher to make it more appealing to your cat.
2. Use double-sided tape to teach your cat where NOT to scratch.  If your cat still wants to scratch places where you don't want him to, you can buy special clear double-sided tape that (usually) won't damage your furniture when it's time to take it off.  Put this tape where you don't want your cat scratching -- he won't like the sticky sensation, and it will help to train him to look for another place to scratch.  But be sure you provide a place where he is allowed to scratch!
3. Trim claws back.  If all else fails, trimming your cats claws can really help.  I take a nail clipper and clip off the point of each claw.  Just be careful not to clip too much, because you don't want to hurt them!  If they are still trying to scratch, you can buy soft clear plastic caps to put over the claws once you've clipped off the tips.  The caps will have to be replaced every couple of weeks, though, as the claw sheds its outer layer.

I don't have much experience with sprays that are supposed to keep cats from scratching certain areas, but I've found that all of the above methods work pretty well.  There is no reason you need to declaw, as long as you are willing to take a little time to nudge your cat in the right direction!