From Disney website:
BEGINNING JANUARY 1, 2010, when you sign up here to volunteer a day of service with a participating organization (and your service is completed and verified) you'll get one day admission to a Walt Disney World® or Disneyland®theme park, FREE! We want to inspire one million people to volunteer a day of service.
Sign up now to receive reminders and exciting updates about the "Give a Day. Get a Disney day."program by clicking on "Get Email Updates" above.
See complete Program Terms & Conditions and FAQs.