For a plane I suggest the APC model which provides 75W square-ish sine wave 60 hz 120VAC power. Cheaper than a computer specific airline seat power adapter and comes with a cigarette lighter plug which comes apart if the seat has an Empower little plug thing. NB the seats are 15V DC so a cheap car version won't work as they run in the 11-13.6V DC range.
Disadvantage over a computer specific adapter is that you have a lot of wires - on for the seat to the inverter, then another the original AC-DC copputer power brick and wires. Sit in a window seat so you can dump the wires on the floor.
AA seats so far are cigarette lighter plugs and sometimes you really have to aim well to plug in. A lot of seats even coach to plug into, check their seating charts - they mark the seats with little black dots.
[This message has been edited by ricktoronto (edited 02-11-2003).]