There isn't any contracts unless you sign up for a special package. Ex: Blockbuster Package: with 3 months of Free HBO and Cinemax and free movie rentals at Blockbuster.
If you go out and buy a Directv System from an online Directv dealer or a local dealer, you will not have to purchase a contract for a specific time period. I did the latter and purchased my system from an online dealer, and I can cancel Directv at any time.
Dish Network has you sign up for 12 months no matter if you have a special package or not.