I surprisingly get a lot of people asking to detail their car. I never intend to make a business of it, but I love doing it to my cars and people ask me to do it to theirs. All it takes is a cheap orbital buffer (mines a used craftsman) and a shop vac. I normally get easily $100 for a basic wash/wax/vac, or $200 to remove scratches and polish then wax the car.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.