There are different types of acne scars: raised scars (keloids or hypertrophic scars), ice-pick scars (small and deep), and depressed fibrotic scars (like craters)
Different treatments work better or different types. There's some good info on scars (and lots of other acne topics) at
http://www.healthyu-skin.org/acne_scars.htm
For example, laser and dermabrasion work best for raised scars and discolorations. Punch excision works better for ice-pick scars. Fat injections can help the deep scars.
Besides the dermatologist procedures, lotions like retin-A and AHAs can cause peeling which will reduce scars, although more slowly.
And time does make scars fade, although REALLY slowly. I also find that drinking lots of water helps my skin look better, in terms of scars and fewer break-outs.