Adsense. With only about 10k hits a day, my bedtime
calculator http://sleepyti.me brings in $10-$20/day. At the rate you're getting users, you could probably bring in a significant load of cash. Good luck!
Thanks for the tip. I saw that article on HN the other day, but the wording is designed to encourage people to leave adblock disabled to see relevant, sleep-related ads. You might be right though, it's always better safe than sorry; I'll look into clarifying the wording there. Wouldn't want to offend my Google overlords!