Ooh Deana, I was looking at putting a quote on my wall too!! You can get these cool decals that come in tons of different fonts and colors and they can say anything you want! (I'm totally not crafty, so 'stencil' is not in my vocabulary!) Here's a few of my favorites:
"A person's health can be judged by which they take two at a time - pills or stairs"
"Movement is a medicine for creating change in a person's physical, emotional, and mental states"
"To feel fit as a fiddle, you must slim down your middle"
"No matter who you are or what you do, you absolutely, positively do have the power to change"
"Living a healthy lifestyle will only deprive you of poor health, lethargy, and fat"