Chemical peels from a dermatologist will pull sun damage out of your skin.
Another option is the Obaji system- it uses hydroquinone (which sort of bleaches out pigment) and retinol (which causes the cells in you skin to turn over quickly, which means that nice, new healthy cells replace the old damaged pigmented cells). It makes you peel while the damaged skin turns over, but that is the price you pay to get rid of damaged cells. It really works. You get that from a dermatologist, too.
Microdermabrasion really isn't going to solve this problem for you, unfortunately. It might help a little, but probably not. Also, non-presciption creams are probably not going to work for you either, at this point. In the meantime, be sure to keep using sunscreen & good moisturizer (I recommend Kinerase). Best advice: go see a dermatologist. They will be able to tell you exactly what to do. Plus, if you've got sun damage, you really should get your skin checked anyway, for any skin cancers that may have developed. (not all skin cancer is Melanoma, and most people start developing lesser-forms of skin cancers by the time they reach their 40's/50's- sooner if you got a lot of sun)
Hope that wasn't too preachy, I just hate to see people struggle with things that don't work when I know there are things that genuinely do!