I just added myself to academia.edu, a social networking site for academics. It doesn’t lay claim on your time like Facebook does with all its little applications – it just displays academics in a tree format, according to their universities and faculties.
The tree format is a little hierarchical, but what I really like about the site is that it allows you to list your research interests. By clicking on those interests, you can see who else on the site is working on the same themes. The site also allows you to publish papers, your cv, contacts, websites and more.