Of course Cancer is at the top of my list. My father died of skin cancer, and a good friend died of a rare bone cancer (she was even denied entrance to the Cancer Treatment Centers of America because her type of cancer was too hard to treat.)
So, aside from cancers, I'd like to cure Progeria-the rare genetic disorder that causes children to age too quickly. People with this disease have many associated problems (such as bone problems, baldness, etc.) and have a very low life expectancy.