Go to a Disney Park on your birthday in 2009 and get Free Admission.
You can register on-line and bring the confirmation e-mail with you to get your free admission. Registration form and details can be found here. If you don't register in advance, you can still take advantage of the offer at the gate, but you will have to fill out forms at the gate, so they recommend saving time by registering in advance.
Already have a season pass or a multi-day ticket that you are planning to use over your birthday. Register anyway. Instead of free admission, you can choose from a few other gifts - a birthday fun card in an amount equal to the price of a 1-day Magic Your Way base ticket for use on merchandise, etc at the park, a special birthday FASTPASS badge for certain attractions on your birthday or a 1-day Magic Your Way base ticket for your use any time until your next birthday.
This offer is not good for children under 3, since they don't require a ticket for admission.