I have to agree with everyone recommending Retin-A. It's proven to be most effective in treating acne, & hyperpigmentation, as well as treating & preventing wrinkles.
It is very strong stuff, so don't go crazy with it. Start on a low dose, applying every other night, & work your way up. Skin can become extremely sensitive when applied too regularly without building a tolerance. Skin may also purge in the beginning if you have underlying acne. I wouldn't recommend applying Retin-A during the day, when you're exposing your skin to sunlight.
Paula's Choice is a great brand on the market with Retin-A in her products {you can purchase samples} & if you go to the website it also provides a lot of useful information. But you should be able to get Retin-A on prescription from your GP or a qualified dermatologist.