Following on the idea of users filling out a form, how about something akin to what we used to use at yaXay? (http://forum.yaxay.com/submitcontest.php) I don't know, it just helps to make things that little bit more 'official'.

Another idea: allow mini-contests. By that I mean those little events just for fun which can be instigated by members or staff. Little fun things that anyone can enter taking as little or as much time over it as they want to give. Signatures, photo captions, creative code snippets, etc.