http://the.wubmachine.com, an automatic music remixing web + mobile app that I built a couple years ago. Still gets anywhere from 20-40k uniques/month. Has native iOS and Android clients, as well as the web app. Ads + in-app purchases generate a couple hundred bucks each month with nearly-zero maintenance, but I'm not sure I have the free time to keep it running indefinitely.

- Costs under $50 per month to run

- Generates anywhere from $200-$1200 per month, depending on the season (it gets big each December for some reason)

- 20,000-40,000 uniques each month

- native iOS and Android apps have ~10,000 installs each

If anyone happens to be interested, shoot me an email at hi@petersobot.com.