Try
www.dropbox.com.
I use it with a number of clients and associates. Set up a folder for your client, they then need to download some software to their computer, share the folder with them, drag and drop files into the folder and away you go. Don't put anything into the public folder you don't want anyone else to see.
You can open Dropbox on your/their pc and work on the files which will automatically update in the other person's folder. You can also view at the same time to discuss any changes etc.
I describe it as a filing cabinet online to which only you and the client have access to a particular drawer via password.
Dawn