I do the change jar, which I believe many people do as well.
I have a separate savings account and all rebate money and other "found" money goes into it.
Twice a year, I clean out the closets and other storage areas. I eBay some of it and yard sale the rest. All proceeds go into the Disney Fund.
I do online rewards programs like MyPoints, CreationsRewards and eBates. All rewards money goes into the Disney Fund. I also participate in online surveys like Pinecone and Harris Poll.
I use rewards credit cards to pay for everything and I pay the balance in full each month. I use the rewards points for frequent flier miles and restaurant GCs. My Disney VISA has earned me $65 in Disney Rewards money since I cashed out in April. DH is self-employed and all business expenses go on a business rewards card. The points and perks from them also go towards getting us to Disney.
I sew. This may not sound like much but do you know how many people don't? There are so many Boy Scouts, Girl Scouts, karate students and dancers that need alterations, hems and patches sewn. The dry cleaner charges a fortune to do it. I charge less. It takes just a little of my time and very little thread to get the job done. Pretty easy money and it all goes into the Disney fund.
I can't say that all these measures have completely covered the cost of my WDW vacations but they have helped to defray the costs significantly.