Here are all the Promo Codes that I am aware of - both past and present:
Codes
Definition
34BEV
3rd and 4th guest free Beverage package
34DIN
3rd and 4th guest free and dining credit
34DINE*
3rd and 4th guest free and dining credit
34KDF99*
3rd and 4th guest for $99 USD
34PHO*
3rd & 4th Guest Free & Photo Package
34SHORE
3rd
Since several new codes have appeared, including some on my own bookings, here is an update:
Codes
Definition
1DINPK
1 Meal Specialty Dining Package
10OFFS
Specialty dining for two, wine trio, bottled water and chocolate truffles
34BEV
3rd and 4th guest free Beverage package
34CHO
3rd and 4th guest sale free
34DIN
3rd and 4th guest free and dining credit