Paula's Choice ClearDaily Skin Clearing Treatment with 2.5% Benzoyl Peroxide
I would apply a thin layer of this 2.5% BP nightly for at least two months, both on my face and back, wait for it to dry completely, then apply moisturizer.
While BP is one of the most effective acne treatments, there are also drawbacks such as drying/dehydrating the skin and staining your clothes. If your skin is the oily type, BP is not a bad ingredient to start with; just be sure to moisturize well to compensate for the dryness that comes overtime.
Oh, and 2.5% is just as effective as 5%, so don't over do it!