Google Docs
Google docs now supports folder structures with nice looking UI. And one of the cool features in docs is if we needs to upload a document we can send that document to give address to upload the document.. i.e. Ludmal-dcjvpd4d-Ahfhrwx5@prod.writely.com (this email automatically generated from google doc). I found this real easy when ever I'm sending a document to the client I can BCC to this address and save all those documents in the centralized location. try your self. http://docs.google.com/