Showtime is offering a one-month free trial when signing up. Credit card required. Cancel before one month and pay nothing, otherwise it automatically renews at $11/month.
If you use RedBox kiosks, here's another deal. Pay $5 at Groupon to get 30 days of Showtime, and 5 one-night disc rentals at Redbox kiosks The Redbox kiosks provide rentals of movies on DVD and Blu-ray. Beware that the Groupon deal also automatically renews Showtime at the end of the first month of service. Note that fees may apply if you keep a movie for more than one night.