Read this page for information on sagging skin. MrsJim sent me the link and it has taught me a lot. Unfortunately the creams, etc will only work on the outer layer of skin. Droopy skin is in different layers, plus muscle. You can do some things to help prevent the overall sagging, but mostly it all depends on your genetic makeup and how much damage you've done to your body with being overweight.
http://www.tuckthattummy.com/anatomy.htm