Just caught the latest new addition to the site and thought I'd expand upon it a little (discounting that range of proposed DC Direct prototype figures from 2000 that never saw actual release for sale):
Although not included in the actual badge set, DC Comics did in fact release a separate Comedian smiley button on its own which sold in copious amounts through comic stores back in the day, moreso than the set (I own three myself):

It was mainly
this Smiley that DC pushed out as so-called 'promotional items' as opposed to up-front merchandizing thus depriving Moore and Gibbons of creator royalties and so starting the feud that, along with rights to the work itself, would eventually lead to Moore refusing to work for the company again - the actual badge set as pictured was endorsed by them and features copies of their printed signatures on the reverse of the display card when you get your hands on it.
Along with the wristwatch (urgh) an official bedside alarm clock featuring a smiley face was also released (I shit you not). These
occasionally show up on eBay.
Three t-shirts came out at the time of original publication as its popularity increased: smiley face (naturally), the Nuclear Kiss skeletons image, and a character group shot in front of an oversized smiley image:
http://bugpowder.com/gallery/tshirts/watchmen.jpghttp://rds.yahoo.com/_ylt=A9iby6GUHe1Gi ... ngroup.jpgAs you say, the six promo posters featuring the individual main characters in original artwork by Gibbons that
doesn't feature in the finished comics are included in the Watchmen portfolio that is still widely available through eBay (a while back, John Higgins himself was selling these via his own site, having discovered several sealed boxes from the 80s containing packs all signed by him, Moore, and Gibbons). Originally released as oversized posters which were distributed to specialist comic book stores which would be stocking the comic in advance of its release in 1986, these feature great character poses and quotes, the best being:
"You know what I wish? I wish all the scum of the Earth had one throat and I had my hands around it." - Rorschach (1975). If you can track down decent scans of these posters, they really would make a great addition to this site for the Watchmen completist.
With all the talk of a tie-in computer game to accompany the movie, don't forget that back in the day of 1987 Mayfair Games released two adventure modules, and later one supplemental source book, based on Watchmen for its
DC Heroes role-playing series. These modules, entitled
Who Watches the Watchmen? and
Taking out the Trash included background information about the Watchmen universe, actually approved by Alan Moore. The supplemental
Watchmen Sourcebook (1990) provided still further background information on the Watchmen universe and its characters. Moore's own approval makes these publications valuable to fans as the only outside source of supplemental information about the characters in the story, especially minor characters such as the Minutemen and Moloch. In 1987, Grenadier Miniatures produced a metal figure set of Watchmen miniatures to be used exclusively with these DC Heroes role-playing games, featuring lead miniatures of The Comedian (with flamethrower), Nite Owl II, Silk Spectre II, Ozymandias, Rorschach, Dr. Manhattan, Captain Metropolis, Hooded Justice, Moloch, and Archie the owlship.
To close with, perhaps one of the more unique items of movie merchandizing will in fact turn out to be for the movie that
never was - the large metal 3" diameter Comedian smiley badge handed out in limited numbers at Comic Con in 2005 and bearing the printed legends
©2005, Paramount Pictures and the
www.watchmenmovie.com addy when Paramount Studios had the domain and ran the site, before their attempt at a Watchmen movie directed by Paul Greengrass fell through and the project finally found a home once more at Warner Bros. Think I'll hang on to my curio Con badge for a while longer... see how much it'll fetch at a later date!