When I first wrote this, I listed all kinds of places. However the site has grown in stature and number to such an extent, that I honestly think here is a very good start, and people whose flats you see will guide you further. Gumtree is still the mainstay with some shortcomings. It's still what everyone falls back on when all else fails. Flatshare sites are still somewhat in their infancy, and there are some shockingly greedy operators who I am sure you've made an accquaintance with. I bet you're not going to be rushing back either.