I'm blessed with relatively good local video stores, so I have yet to sign up for any service ala Netflix myself. That said, I've heard good things about GreenCine.
I briefly used the Blockbuster online service. I really liked it, but cancelled it temporarily while I'm out of the country. The advantage to Blockbuster is that they're fast, and they give you vouchers for two in-store rentals each month, which is nice.
