Melasma can be difficult to treat and someone with intense melasma should understand it is not always possible to remove discoloration completely. BUT...blending melasma-affected skin with lighter surrounding skin is possible.
There are several excellent products and programs. Obagi, Cosmelan, Spot Peel, various other de-pigmentation peels and home programs all provide different levels of improvement.
Melasma will always appear more obvious if you don't practice consistent sun protection. And by consistent, I mean every day - rain or shine. A full spectrum sunscreen or sunblock should be on your face every morning and reapplication (if possible) is recommended.
Like acne, Melasma should be viewed as a chronic condition that is managed more than cured.
Web reference: http://www.rebeccafitzgeraldmd.com/cosmelan.html