Free companion ticket with round-trip purchase from American Airlines

At American Airlines, earn a free companion ticket when you book a round-trip flight between the U.S. and the UK. It's one of the best such offers we've seen from American Airlines. The companion ticket is valid on a future flight to the UK or to the Caribbean. Initial flights must be booked and traveled by March 31; companion flights must be booked by June 30 for travel through December 31. Click here for complete details.

Also of note, British Airways is offering free companion airfare to members of its Executive Club frequent flyer program who book a qualifying round-trip flight and travel by March 31. Visit British Airways' Executive Club page to join the frequent flyer program. Once you've joined, you can register for the offer.