I hate flies too. Fortunately we have two cats who like to eat them. (I don't like the sprays - too smelly and full of nasty chemicals for my liking).
Have you tried getting one of those stickers? You put it on the window and they get attracted to it, thus splatting themselves. They peel off quite easily afterwards, too, so you're not left with a Damien Hirst-esque display in your lounge.