Consumer Reports, Lisa Lee Freeman said, "One of the best-kept secrets is discount codes or promo codes, which you can use to book your tickets online. You simply enter a string of letters and/or numbers and you can save 10 to 50 percent on your seats."
Recent promo code offers include up to $175.00 off a Delta vacation package to Hawaii. For a U.S. to New Zealand and Australia flight -- 20% off. And from United Airlines, a free flight if you bought a ticket on certain flights departing from Denver.
Freeman said, "Airlines come up with promo codes to drive people to their websites and bypass sites like Travelocity and Orbitz, where they have to pay a commission."
Along with airfarewatchdog -- farecompare.com is another good source for codes. With both sites, you sign up to get alerts for deals.
Be aware when you sign up for airline promo-code fares, your inbox could get flooded with deals that don't interest you, so it's a good idea to have a separate e-mail account.
"Another way to find promo codes is to do a web search and put in the name of the airline and the words 'promo code,'" said freeman.
While finding the codes isn't always easy, Hobica says it's worth it. "It is a lot of work to find a low airfare, but it doesn't take that much time and it often pays big dividends."