http://www.seatguru.com/
I spend way too much time on airplanes (I have nearly 2 million actual miles on Delta alone), and my company is great about allowing me to fly business class on long international flights. I wouldn't be without Seat Guru, which has virtually every configuration of airplane on most, if not all, of the airlines in the world. You can go into this site and see where the good and bad seats are on your flight, and make/change your reservations accordingly. If you fly a lot, this is a great tool.