I've assembled a comprehensive list of Marriott promo codes which are intended for the 'general public'. This list can be found at http://www.rentalcodes.com . Select 'Marriott' from the dropdown box under 'Hotels'. To make this list easier to search, i've eliminated company-specific corporate codes.
I've also checked each code to make sure it is current and have eliminated outdated and obsolete codes.
I've also added a number of codes not found on this forum. Hopefully this will make your searching easier.