The Walt Disney Company this year has a promotion that offers everyone free admission on their birthday to either a park at the Disneyland Resort or a park at the Walt Disney World Resort. The admission is good only on the exact date of the person's birthday (valid proof of birthday is required), and if the person already has admission media (like an annual passport, for instance), then they can choose among a couple other offerings instead.
Here's a site where you can register your birthday with the Disney company. It's not required to register to get the free admission or other perqs, but it certainly doesn't hurt.
I've already decided that for my birthday, I'll be opting for the gift card in the amount equal to one day's single park admission. I haven't decided what I'm buying with it yet though.