The best discount you can get is the AP discount (anual passholder). Other discounts would be DC (Disney Club), AAA, Am Exp, and other various codes. Keep your eye on http://www.mousesavers.com
Discounts from codes have been ranging 30-40% off rack rate. AAA discounts can range from 10 to 20%. I believe Disney Club discounts fall into the same range as AAA.
This year, 30% was the discount for Annual Passholders.