Standing around and letting university or college students draw you sounds like it's both boring and embarrassing, until you realize that someone's willing to pay you to do it. Your time is worth money. Most classes that go looking for subjects for their students or members to paint will pay something in the region of $15 per hour for you to be their muse.
This might not make you rich on its own, but it's a great way of making extra money that you can fit around your working life. Work regularly with one or two institutions in your area that require life models, and you'll soon earn enough to buy your way into one of the other money-making methods on this list! Plus, when you think about it, it's kind of flattering. You could always offer to buy back some of the better work and hang a portrait of yourself on the wall.