These days, getting a good deal on airfare is as much about where you book as which airline you fly.

Airlines are offering more exclusive deals and discounts to travelers who do business directly through their web sites, instead of by phone or through a third-party travel agent site, such as Expedia (EXPE), Orbitz (OWW) or Travelocity.

Struggling airlines are offering these deals in an effort to build customer loyalty and avoid paying commissions to other sites and companies for selling their airfares. "There s a lot of money to be made, and they want to be the ones making it, says George Hobica, the founder of AirfareWatchdog.com, a site that tracks prices on air travel.

Transactions conducted over the Internet also offer airlines cost savings because they don t require an employee like a ticket agent to take calls over the phone. Keeping people off the phone is so much operationally cheaper, says Rick Seaney, the chief executive of FareCompare.com, a web site that aggregates travel deals.

Of course, every fare is unique, and many third-party vendors can still undercut prices that appear on airlines web sites. Expedia eliminated its booking fees in June, and Orbitz and Travelocity have extended sales that waive their fees. Without those booking fees -- and with site sales in play -- travelers may still find cheaper prices than airlines are charging.

Keeping on top of the latest airline-exclusive deals is as easy as signing up for the frequent flier clubs and e-newsletters of the carriers you use. Be on the lookout for these five lures:

Fare Specials

It s not unusual for airlines to offer weekly specials that trump offerings on third-party sites. WestJet, for example, is running a 50% off fare sale to select citiesFor more ways Twitter and Facebook can save you money, click here

Package Deals

Airlines have edged into the broader travel business. Buy a flight and now, they try to sell you a rental car, a hotel and travel insurance, too, Hobica says. Such packages offer substantial savings. For example, through July 31, Delta (DAL) is offering airfare and three nights at The Venetian Las Vegas (where rooms regularly top $250 per night) for as little as $332 -- and that s before you take advantage of promotional code DV10621 to knock off another $50 at checkout. (For more details, and other casino-destination deals, click here

Mile Bonuses

Promotions that push travelers closer to award travel keep them coming back, Seaney says. This spring, American (AMR) offered 25,000 bonus miles on round-trip coach flights to the United Kingdom. (Business and first-class passengers received 50,000.)

Promotional Codes

Online retails aren t the only ones to offer coupon codes for a discount at checkout. Users who enter the code 75WESTIN at their checkout will save $75 on Southwest (LUV) packages of a flight and three nights at a Westin hotel. Users who enter their frequent flier number into the Hawaiian Airlines deal page will get an electronic certificate good for 10% off their next round-trip fare to Hawaii booked through the site.

Discounts on Fees

United (UAUA), US Airways (LCC) and Delta all knock $5 off their checked-bag fees (regularly $20) if you check in the bags online. Through August 31, Continental (CAL) is awarding 500 bonus frequent flier miles to consumers who make changes to their itinerary online instead of calling the customer service line. (Users will still pay the $150 change fee on domestic tickets.) Seaney says web incentives are gaining popularity among airlines. You re going to see a lot more like that, he says.