PointsHound is a website that will give you frequent flyer miles for making hotel bookings.
They will give you 100 miles just for signing up (this is my referral link — the 100 miles comes from being referred by an existing member, and the referrer only gets points when a new member actually makes a booking through the site — if you’d like feel free to add your own referral link in the comments).
You can choose earning miles with United, Delta, Hawaiian, and Aeromexico.
And while many websites like TopCashBack and eBates will offer cash back for the hotel bookings you make through the hotel’s own website, PointsHound rebates you in the form of miles and has you book through their own system.
The downside to making bookings through third party websites is that some chains do not allow accrual of elite stays and nights for those reservations, some do not allow points-earning, and still some do not even offer elite status recognition. That’s why I’ll almost never make hotel bookings through Expedia or Orbitz, for instance. Still, the rebate value here (paid out in miles) looks reasonable overall.
The more bookings you make through the site, the more miles they’ll pay you per booking. New customers earn “around 4x” miles while after booking 5 room nights you earn “around 6x” and after 20 nights you earn “around 9x”
I don’t expect to use this site often, but for non-chain hotels (since I’m less concerned with status) it could be very useful. And it’s certainly worth 100 miles for signup since they require just your name and email address to enroll.