Disney frequently offers ways to get a free one day pass. Last year (2009), you could get in free on your birthday, and this year (2010) you could get a free pass for doing a day of volunteer work. While Disneyland isn’t offering a way to earn a free pass at the current time, it is most likely they will again in the near future – so stay tuned.
Often Disneyland offers ways to get extra days in the park for free. Currently, if you buy tickets on the Disneyland website, you can get 5 days for the price of 3, and 6 days for the price of 4.
You could also get free Disneyland tickets by winning them though a sweepstakes. There’s several sites that keep up-to-date lists of upcoming Disneyland sweepstakes – where you fill out a simple form to enter.