I use a stereo pair of DPA 4060s clipped to the outside of a bag (this ensures they are about 40cms apart) going into a Sound Devices 302 mixer into an Edirol R09 recorder, both of which are inside the bag.
These are the clips I use:
I haven't used this setup specifically in an airport but I have used it in various other public spaces with restrictions on recording. It's very stealthy, unless someone happens to look inside your bag whilst you're adjusting levels, and you get very high quality recordings.
I have used the Edirol R09 on it's own in airports, which gives decent enough recordings but they don't have much width or depth.
One thing to note, which I'm sure you haven't overlooked, is an airport has to be one of the worst possible places to be caught recording illegally in. The main reason I haven't used my stealth recording rig in an airport or on a plane is that I generally don't want to be seen fiddling with a bag full of wires and flashing lights in those places.