I started using a product that another cyster here recommended called Carley's, and it's much cheaper than Proactiv and from what I understand, pretty much as effective. It contains 2% benzoyl peroxide and the rest of the ingredients are natural. Here's the website if you're interested
http://www.no-acne.com/main.htm (contains a complete ingredient list), and they also have auctions going on all the time on eBay. I think it runs $24 with shipping (for 16 oz. bottle).
They do offer a money-back guarantee so you're safe if it doesn't work for you or you don't like it. I am on my 3rd bottle and I ordered my first one back in Feb. '02 I think. I didn't have really bad acne (mostly just scars now from my teenage years!) but I really like it and use it every day. My face stays clear.
Anyway, no I don't do endorsements for these people and they don't pay me

I just like the product.

Hope that helps!