Our big three savers...
Annual Passports. We lived in the Kansas City area, were 1265 miles away and drove every trip, but still stole incredible value by getting annual passports. We got them two different times. The last time (2008) our trips amounted to 10 days in the parks late summer, 6 days over New Year's, 6 days during spring break, and another 10 days in the parks in the early summer. That translated to a daily ticket cost of just over $15 per person.
Sleep outside of Disney. We stay at places that are just about as cheap as possible, but still close to the WDW entrance. The cost was half of Disney value resorts and we got breakfast (even if it was just cereals, bagels, (bad) danishes, juice and milk).
Get the majority of food outside of Disney. We went back to the hotel in the afternoon almost every day in the summer and about half the days of the other two trips. During those breaks either my wife or I would run to the store for supplies. We got stuff for snacks throughout the day, as well as things for lunch and/or dinner. Sandwiches, hummus and pita, lots of veggies and fruit, and anything we could find and tolerate for microwave eating. I know what you're thinking--we must not like food. In fact, the exact opposite is true. We're big time foodies. We just don't find value in paying Disney prices for theme park food. The exception is at Epcot where we purchased something to eat every afternoon/evening, whether it be a meal (always a late lunch for the cheaper prices) or a delicious treat. Oh, and a meal in Cinderella's Castle.
Yes, all of these things are extreme budget-conscious decisions. We found it was worth it. For our family of four, we had four trips totalling 32 days at the park, 2 days at the beach, and 8 full days on the road, and it cost us around $5800. Friends of ours went for a week and spent just $1000 less than us. They stayed and ate at Disney the entire trip and loved it; that wasn't for us, though. We willingly pinched every penny to get as many days at the parks as we could.