Love zip.ca
It's not good if you're after the latest blockbuster that just came out on dvd; there's a queue in which you'll probably wait up to 6 months for something like the latest Batman. If you're more interested in offbeat, cult or hard to find titles than you'll love it. I like to catch up on old movies or movies I saw ages ago (and you can't see anywhere anymore). The trick is to treating it like having a nice surprise in the mail instead of expecting/ waiting for a specific title.
Tip: If you want to maximize your bang for the buck, find a way to "backup" the movie so you can return it right away and watch it at a later date.

I think it works out to about $2 a movie which I think is a good deal.
As I mentioned you'll still need to go to your local Blockbuster to get the latest releases.