A little while ago I posted about this to webcomics but didn't get much response. Since then I've created a Fan Fiction page and category at Comixpedia, a webcomics wiki. (Is there an equivalent fanfiction wiki?)
To somewhat repeat my post: The huge majority of what I have found is to some extent a continuation of the japanese culture of "Dôjinshi" fancomics. It's possible I'm just looking in the wrong places but afaict there's not much of a culture of writing fancomics based on two of the the non-manga staples of both webcomics and fanfiction, ie fantasy and science fiction. Stuff like Star Trek and Star Wars etc.
Anyway: is it just that I don't know where to look, or is there simply not that much of this sort of thing out there? Or there is, but they're not organised? Any ideas as to why the genre isn't more popular? I mean personally I'm not that desperate to read it(*), I'm just curious.
(*) I think I'd prefer comics based on my favourite books (the Vorkosigan Series for example), but given how little fanfiction there is for those I think expecting comics would be overly optimisitic! My excuse for going to so much effort for something I don't actually care about that much is that finishing my Phd has left me with excess research energy :)
EDIT AGAIN: Wow, thanks for all the examples! If there's any more and you're feeling really enthusiastic you can create a page about the comic (adding it to the Fan Fiction category of course :))
EDIT AGAIN AGAIN: So someone deleted the links, and I guess it was getting a bit long. Having nowhere else to put them, I put them on my user page. Also I made a page at fanlore (which, if you're reading this, is probably where you've come from. Hello :))