Disney is offering a free One Day/One Park Ticket to those folks living in the United States or Canada that are 6 years of age or older. (They have a limit of 1 million tickets, but many folks don't think they will reach it).
You must first start by going to the official Disney Parks website. (On or after January 1st, 2010)
http://disneyparks.disney.go.com/disney ... Disney-Day
You must register, and then pick one of the Volunteer opportunities listed at their website. After finishing your required participation, you will receive an special e-mail with a barcode to take the park Main Ticket Windows. They will process your paperwork and give you your free ticket. See the above link for full details and rules.
The Volunteer locations are located all over the USA and Canada, so you can do your "day" prior to arriving in Anaheim, in fact, you should do it a few weeks before you arrive.
Also, if you have a Multi-day ParkHopper (such as buying a vacation package including staying at HoJo's and getting Disney Tickets) or an Annual Pass, there are alternative "gifts" you can take advantage of. Check the link above for all the info.