Disney used to have a program called the Disney Club, which got you mediocre discounts on dining, merchandise, park passes, and resort rooms. But DC was axed a year or two ago.
The most popular Disney discount card these days is the Disney Dining Experience, which gets the card holder about a 20% discount on most sit-down meals at WDW restaurants. The catch is that it is limited to Florida residents, and WDW Annual Passholders. To Florida residents, the DDE card is $75 a year, and to Passholders it's $50 a year. It is a bargain, however - I know of people who have made the DDE card pay for itself in a single 1-week trip.