Buyoyo (used to be called Layoyo).
www.buyoyo.com[url]
They have the cheapest prices I've encountered, and I've never had a problem with their service. (For the first time in the several years I've been buying from them, I've had to return a disc that was defective. I'm in the middle of that process. If I encounter problems I'll re-post.)
One tricky element is that all their prices are shown in HK dollars, but they have a translation option that will give the price in the currency of your choice.
One negative is that they tell you next to nothing about the movies. It's not a good browsing site, especially since the actors/directors names are written in a different format - the best way to find Stephen Chow movies, for instance, would be to find one you know then link on his name. But once you've identified a movie you want to buy, this is a good site to purchase from.[/url]