I was going to say, I find the fly-swatter most satisfying! Esp. those electric ones!
Can you maybe check the attic or basement for a passed away critter? I know it sounds gross, but sometimes it happens.
I also have heard of bags of water hung from doorways and windows, whatever entry points. They should be hung where the light shines in. It has something to do with the fllies not liking it because of the light refracted off of them and their funky eyes. I have friends that swear by this and use them in their horse stables and on front porches.