There's also leaving your body to a medical school or using a company that provides bodies and organs for surgical practice or medical research. As I understand it, medical schools just don't have enough practice cadavers because people don't think to donate themselves for medical study.

Also, you can get your body cremated after use and the ashes returned to your family once your body has been used for SCIENCE!

I think there are other companies, but here's one I found in a quick Google search: http://medcure.org/why-body-donation/