Let other sites „be your website“
This is a strange but rather interesting idea: Modernista, an ad agency, doesn’t actually have a real website. Instead, the just provide a navigation layer that sits on top of various websites that have the relevant content, i.e. a flickr gallery of their work, a google news page with news of the agency, a wikipedia page (or facebook profile) with the descriptive info of what the agency did in the past and offers for their clients.