Online booking bonuses.They come and they go as the airlines try to lure customers away from middle-men, and it’s not always easy to keep track. For the moment, there are still a few good deals out there.

Southwest, of course, tops them all with its Freddie-award winning double credit for online booking. Getting a free flight in as few as four roundtrips is nothing to sneeze at. And it’s currently been extended through the end of the year.

Perhaps lesser-known, but almost as valuable, is US Airways’ first-time online booking bonus for 3,000 miles.

Sure, the bonus drops to 1,000 miles after the first time, but it’s the best that the Big Six have to offer. It ends July 31.

American AAdvantage, Continental OnePass, Delta SkyMiles and United Mileage Plus all offer 500 miles for one-way bookings and 1,000 miles for roundtrips. All are ongoing except United’s, which ends Sep. 30. American’s applies to award booking online, as well.

Northwest WorldPerks is the stingiest of the big guys, with a 1,000-mile bonus for first-timers, and 500 miles after that. Northwest’s promotion ends July 31. In the interests of disclosure, though, it should be noted that WorldPerks also offers a 1,000-mile bonus for booking award travel online for the first time, through July 31.

Of the smaller airlines, only America West is offering an online booking bonus, at 500 miles per roundtrip.