There's also a product called "Stickypaws" which is, essentially, like double-sided tape, that you can stick on the areas of furniture that your cat likes to claw...they don't exactly ENJOY touching the sticky surface and in very short order will leave the furniture alone. We tried this "peel and stick" product (available in regular pet stores) with our last two cats and they learned to go elsewhere for scratching and have left the arms and legs of my furniture alone since!

Chatty's suggestion of nail covers works well too - I know a few people who use those.