<img src="http://www.xanga.com/images/winky.gif" class="emote" alt=";)" />
which works just fine. Why do I use Xanga emoticons? Well, despite how ugly they are, I prefer them to text-emotes. If I found another service with easily-accesible emote images I might switch to using them.
The idea, then, is to make a greasemonkey script that runs on clicking 'Publish Post' and automatically goes through and replaces certain emote strings ( ;), :), :D, :P, etc ) to the appropriate image-tag code.