Jess - I get a lot of my motivation from sick people as well. I have lost 3 granparents to cancer and my mom is a breast cancer survivor. Knowing that I have a predisposition to cancer really motivates me to be the healthiest I can be. No, it's not a guarantee that I will always be healthy, but at least I know I am doing everything I can.
I am also motivated by the feeling I get when my body is strong, the fact that I feel so much more energetic when I don't fill my stomach with crap, and how much better I feel going out when a layer of fat isn't spilling over the top of my pants. And I'll say it since no one else has - I love not being embarrassed to be seen naked and having so much more confidence when I am!
Those are all of the things that keep me going...