Travel off-season. Think cities in winter and ski or Caribbean destinations in spring.
Book flights early -- or late. When an airline's limited number of low-price seats sell out, fares jump. But if you can leave on a few days' notice, you may be able to snag a deal: Some airlines lower prices to fill empty seats. Call each airline or check their websites. You can also try CheapTickets.com Try an alternate airport. For instance, instead of San Francisco, fly into nearby Oakland; for Miami, Fort Lauderdale; for New York City, Newark, NJ.
Stay Saturday night. Airfares are a bit cheaper that way.
Log on to airlines' websites after midnight -- when they update their specials -- and check back daily. Many of them also let you register to receive regular e-mail updates on current deals and promotions.
Ask the hotel for the cheapest rate. It sounds obvious, but do it anyway. Mention any memberships, such as AAA or a professional association. You should also ask about a "family plan" -- you may be able to get a second room at half price.
Track down local deals. Some popular U.S. destinations are served by CityPass.com