a new guppie, welcome! first of all, just to prevent it from getting worse, try to wear clogs or mules in the sun…something that covers the whole front of your foot.
i would recommend using something to get rid of dead skin first, something like this:
How to Fix Cracked Heels with Stridex | eHow.com
maybe the stridex pads would work on the top of your feet and you could cover that with lotion?
i dont know about whether this would work on the feet, but Shiseido White Lucent line sure does work on the face. their brightening serum is really expensive, so you could always get a sample of it from sephora first. however, maybe you could try a cheaper brightening serum. there are lots of brands out there.