Are you talking Colonial Wburg or Water Country/Busch Gardens?
For Water Country/Busch Gardens, you can get coupons at all the McDonald's down in the area.
Also if you go to Water Country, then in the park you can get a discount ticket for Busch Gardens the next day, before you leave Water Country. (And vice versa, but WC is cheaper than BG to begin with.) I'm pretty sure this was less expensive than buying the two-day pass for WC/BG.
For Colonial Williamsburg, remember they give discounts for teachers and the military.