Livejournal is the one I use the most, but I don't know if it's possible to do it for multi-chapter works on that site. It's got a very different feel to it than ff.net or twilighted.net, as it's journal pages with graphics rather than text-based.
Here's a page of a longer work on livejournal, if you want to check it out:
http://community.livejournal.com/plotamari/3575.html
But honestly that's just a feeling I have about the site - I'm no programmer, just an ignorant user.
