Even though too late for the OP, I am posting this Sea World discount link just so the thread will be complete.
http://dealspl.us/seaworld-coupons
There are many other sites, and a web search on for sea world promo codes will pull up a ton of them, but you have to be aware that some are specific to a single Sea World location.
In addition, pretty much any one-day ticket to Sea World Orlando includes a second day free. You have to go to a window just inside the turnstiles, to your left, to validate the second day.
Also, to use a promo code on Sea World's web site, the first thing you have to do is click on a link at the top nav bar to "promo code" to enter it, and then go to order tickets. There is no opportunity to do so in the shopping cart.
See also:
http://www.mousesavers.com/seaworldorlando.html