You can gain a little bit of extra power by installing an underdrive pulley on your engine. They are made of billet aluminum and lighter than the stock pulleys. The reduced weight can give up to 15% power increases. They can also help by running the accessories attached to your engine at a slightly slower speed, so your engine doesn't have to work as hard.
Be sure to purchase a well respected brand. This is not a part you want to be cheap on, as purchasing an unbalanced or defective one can cause serious damage to your engine.