I bought a prescription mask for snorkeling before I started diving from Deep Blue. You can see it on my picture to the left. It was fairly inexpensive, it never fogs and other than an uncomfortable pressure point on my forehead (which I barely notice while in the water) they fit just fine. Also, I never have more than a few drops of water get in even though I have a mustache.
I have spent a lot of time in the last year looking into options for a new mask with 'scrip lenses. Because I am farsighted there are few options for OTC masks with replaceable lenses. Tusa makes one with lenses in my strength, available from Amazon, but I returned the mask because it was smaller than my Deep Blue and I really want larger. It looks like my only other option is to order through one of the custom lens outfits that others have mentioned, but they are pretty expensive. For the time being I'm sticking with what I have.