Proactive, the widely popular acne line, uses two very common ingredients to fight acne: Benzoyl Peroxide and Glycolic Acid. While there is no doubt that Proactiv is affective for many, let's not forget that there are more affordable products on the market that will give you similar results. (As well as the ability to shop for them when you need to restock, instead of having them ship automatically.)
If you have been thinking about purchasing Proactiv, but you're not sure you want to spend a lot on your skin care regimen, you must check out the article, Is There a Cheaper Alternative to Proactiv?, buy About.com's Guide to Acne, Angela Palmer. You'll also get more product recommendations by reading her Benzoyl Peroxide Cleansers for Under $15.