I'm also into using lists to store game graphics and sounds instead of arrays so that when I want to assign a graphic or sound to a sprite I can refer to it by name instead of an integer value or constant which may have to change as you grow the game (which is a pain).
I tried that a while back too, grey. You have to remember there's always a reference to the image left if you're trying to get rid of images from mem. Stumped me for a while that one, but yeah, your way is a very nice, simple, elegant way of doing it. bmx does rock.