When I went to cancel, I was presented with an 800 number to call to complete the cancellation. It was here that they offered me 50% off.
I signed up for the 4 movies a month by going to 'Your Account' and clicking 'Upgrade or Downgrade Your Membership'.
I've been a member since December 2001. Interestingly, on their website under 'Your Account' you can view your 3 month rental history and request they email you your entire rental history. I'm doing this to figure out my actual per-movie cost.
edit: FYI - just figured out my average cost per movie since I joined - $5.26 each. Granted, I've had a bad habit of letting movies sit for a month or more unwatched, and back in my Blockbuster days I paid my share of late fees, but it's definitely something to think about...