I'll sometimes read a book when on the stationary bike, squats or jumping jacks when waiting for something to cook in the oven/stove/microwave, playing / strength training with my 15 lb bichon frise(he thinks it's great fun!), taking said bichon frise running on a leash beside me when I go out on my bike, hula hooping with my weighted hoop while watching one of my shows, doing the "washing machine dance" when doing the laundry(okay, I admit I'm a major dork...), and dancing while cleaning house('tis great fun to some music when you're mopping

).
Edit: I thought of another one! Using my stability ball at my desk instead of my desk chair and doing exercises on it while waiting for pages to load or taking breaks from my studies.