1) Book your hotels through Hotels.com. For every 10 nights you stay, you get a free night (valued at the average of the rates you paid over those 10 nights). I just got $154 off a booking in Key West. If you use the site regularly, they’ll upgrade you to their FiveStar service. I’m not sure exactly what that means, but the other day when I called the priority customer service number, I got to speak to a human right away.
The other benefits I like from hotels.com: while you do have to prepay for the booking, it’s almost always refundable following standard hotel policies (i.e. 24 hours prior). Most other sites only offer nonrefundable bookings if you want the best rate. Be sure to read the fine print on this, though, because each hotel is different. (I’ve booked close to 20 hotels with them, and they’ve all been fully refundable.) Also, they have a price guarantee: if you see your hotel offered on their site for a lower rate at any time, call or email them and they issue a refund for the difference. I got a refund within 24 hours.
2) Sign up for hotel loyalty programs, even if you don’t intend to stay there regularly. You’ll be surprised at the number of small hotels that are actually affiliated with one of the major brands. Most of those programs allow you to convert points to airfare instead of free stays.
3) If you know there’s no chance of your trip being cancelled, get a prepaid rate. They’re almost always lower.