Some call them Rewards Programs...some call them Membership Programs. Either way, if you pay attention you can gain some great benefits. Budget Travel just had some great info on programs. Here are some of their findings as well as my own information.
Southwest Airlines Rapid Rewards: fly eight round trips within two years and receive a free ticket. You have up to a year to redeem this ticket. Not a bad deal if you fly Southwest often enough. Plus it's easy to use, there are no cancelling fees...and your bags fly free. This one makes a lot of sense for those of us that love Southwest Airlines.
Delta Skymiles: fly 25,000 miles and your rewards start. Since it's more of a challenge to find a ticket for your 25,000 miles you need to book early. Start as soon as you know you will be traveling...up to 331 days in advance!
American Airlines Aadvantage: fly 25,000 miles for your free ticket. Relatively easy to book online this one also allows you to use your miles one way (first class for instance) and then pay for the return trip. Might make a difference if you are flying a long distance.
Marriott Rewards: spend $750 (7,500 points) and you will earn a free night in a category 1 hotel like a Fairfield Inn. A free night at a category 7 hotel requires 35,000 points ($3,500). This is a good deal if you stay often enough at Marriott Hotels.
Hilton Honors: earn hotel points and airline miles for the same stay if you like. Your points equate to dollars spent at all Hilton Hotels. This one is easy to use.
Starwood Preferred Guest: Starpoints equate to every dollar spent. You do need to book these over the phone, however.
If you are staying in hotels frequently, try to stay in one brand that you like. Join their membership program and get your points to work for you. It doesn't cost anything and who doesn't like to get a free room in a hotel you might not have wanted to pay for...especially for a special treat.