Facebook, Wordpress, Tumblr. I have a twitter account, but until I have a smart phone, it isn't enough fun to use.
I found that Facebook and Tumblr drove viewers to my blog, while Pinterest didn't do anything for me. I have a website planned, but I haven't felt a real need to do it yet, at least, not until I get more than short stories published.
As a previous poster asked, I used LiveJournal back when I was doing fanfic. I haven't really used it since.