For British users here, MovieMail is surely best as you can rent as well as buy by mail order. The rental system is indispensable. Years ago, i used to buy some from Mr Benson's (mentioned above) but this is a far better and more knowledgeable company, specialising in world cinema, though they do have all the stuff that's available in the UK. Check out their website (they do catalogues 2x year and regular newsletters, too, have some top writers, and one whose taste is flawless); http://www.moviem.co.uk