I believe DVC gets a discount but I am going to guess that you don't have DVC.
Other than that, there are no discounts on the annual passes. The only known way is to buy a discounted MYW ticket, use it once, and then upgrade it to an annual pass. Right now I would have to say that the buy 3 day MYW w/ park hopper get 2 free at Orbitz is your best deal. And if you do Ebates, I believe they are also giving 20% back for that purchase.