Most hotel chains offer membership rewards programs that can really be an advantage to frequent travelers. These memberships are free to join and automatically keep track of your nights spent at participating hotels and motels to add up to your rewards.
If you are using an online booking service such as Travelocity, Expendia, Orbitz or Priceline be sure to compare more than one. Often hotels are listed exclusively with one service and don't show up on them all.