Well how exciting. In my search for info that nobody else cares about, probably I have discovered that the original four emoticons were :) :( 
and 
People were asking for grr and blush in 2004 but they didn't appear then. Bold, italic and underline started in 2004, though, and you could only do single words at a time (I remember that remaining for strikethrough for ages). This was due to a fear that people would randomly bold things they didn't mean to like swearing.
The wink was originally made by typing ") but that kept being triggered accidentally, so they introduced the square bracket codes. That annoyed people so they reinstated : ) : ( and : o as shortcuts, but not ") and for some reason not ;) either.
added in June 2004 by Tech2, without shortcuts. And all original 4 tweaked/updated. But the new "wink" was apparently a bit creepy so they reverted to the original.
came in September 06 without much fanfare or announcement. A poster called SpaceDonkey/Reginald was credited with drawing emoticons, perhaps the older ones too.
Christmas smilies first added in Dec 06, the drawing of the hats was outsourced to a MNer called SaintGeorge - SpaceDonkey again?
Then the ones I remember - 
in 2009 (hugely controversial) originally intended to mean "I have nothing to say on this matter".
apparently broke the site when it was launched and needed work. This is the original: www.mumsnet.com/bigtech/10.gif It's not really clear when it actually launched as there are just a few posts mentioning its brief appearance in early 2009 around the same time as the biscuit and then Justine saying it was in the works but not yet released, and then it starts being mentioned in 2010 as though it's part of the normal list. I do remember a massive thread about it at the time, but possibly it was in chat.
Here's another deleted/secret one from BigTech: www.mumsnet.com/te/bigtech/blank.gif
Yes, I could have been doing a number of more useful things with my morning.