Blockbuster.com has their online rental service $10 for your first month, then $17.99
per month. You get one free in-store rental (games included), unlimited online rentals (3 out at a time) with free shipping, no return dates.
You can return your online DVDs to a store and immediately receive a free in-store rental in exchange. They will also count that online DVD as having been returned, and proceed to ship the next DVD in your queue.