Moviemail (http://www.moviemail-online.co.uk/dvds/) has all the foreign language dvds anybody could reasonably want. Not necessarily all that cheap, but their monthly email catalogue is also a great place to look for obscure stuff which you can then buy at Amazon (also not a bad place for buying dvds!) or rent at LoveFilm. The Auteurs (www.theauteurs.com) has loads of foreign movies for streaming if your broadband is up to it.

Once or twice in the past, I've used Amazon's continental branches Amazon.fr and Amazon.de to get hold of foreign language titles that weren't available elsewhere - though obviously you need to check whether the titles in question have English soundtracks or subtitles on them if you're not a fluent speaker of the language in question! Many French DVDs in particular don't seem to bother with English subs. Movietyme (www.movietyme.com) can also be quite good for various South East Asian titles, especially on Blu Ray.