If you're looking for titles which are unavailable through Netflix, out-of-print or imported*, you should try Facets Multimedia in Chicago, Illinois. I rent movies from them by mail, on DVD and VHS**. They have a subscription service identical to the Netflix model (except instead of a queue, you have "selections"), and the prices are the same**. Allow an extra day or two for your selections to arrive, since they come from Chicago.
For imports, you need a multi-region DVD player.
**The VHS rentals incur an extra shipping charge.