I got the cheapest one I could find from Argos. I think it cost me about £10. I went for one with a couple of flat pockets, to keep my paperwork & maps separate, several pen pockets, a couple of zip-up pockets for the little bits you always seem to lose, and space for a headset, kneeboard & hi-viz jacket in the main bag.
Recently I've only been flying a cub & my microlight, so I have a HUGE bag ... full of warm clothing.
