I second the goal idea! Huge motivating factor for me!
As for getting sick, every time I've started an exercise routine I have always come down with strep or Bronchitis shortly after starting. I think the initial taxing of the body may mess with the immune system, though eventually the opposite is true. What I did, and this may sound strange, is I would go through the routine of getting up, dressing and going to the gym just to keep the routine. I turned right around and went home, mind you. I didn't want to get anyone sick. But I had to keep the routine. After a year, illness is no longer a derailer. I get really anxious to get back at it. Perhaps when you're sick you can still get up at the time you should, dress like should, and then turn around head back to bed.
Other motivators: Clothes come to mind. This from a non-typical woman who doesn't care so much about clothes! LOL! But I have come to like workout clothes. It's bad. Very, very bad. I just bought my first pair of spin cycle shoes and couldn't sleep the night before, I was so excited! Two weeks later and I still can't wait to hop out of bed and spin in them. New music for my ipod. I find the class environment extremely motivating and I can't wait to go in the mornings.