Yes, you can escape from the knee-crunching confines of regular economy class. And you can do it without raiding your financial portfolio to pay for first or business class. Several big North American airlines plus KLM offer "semi-premium economy," or several rows of regular economy seats with added legroom.

You generally get the same cabin service as regular economy, with a few extra perks on some lines. As an ordinary traveler, you can buy your way into these extra-legroom seats when you reserve your ticket or just before departure, on a standby basis. If you're a high-ranking frequent flyer or you paid full-fare economy, you might get in for nothing extra or at a discounted price.

(Sample fares listed are based on a comparison for midweek flights in February 2013. Seat measurements were found on SeatGuru or the airlines' websites.)