The get the 3rd day free with Discover program was broadly advertised at the ticket booth. This saves you about $15 over the standard admission price. While this seems to be the best (non southern state discount) the 3 day Discover passes expire within 30 days so you have to make sure you are staying that long.
I know you can get $5 off the regular non-exipiring 3 day pass buying over the web, and you can get $10 script with entertainment book.