I remember seeing a brilliant site that provided a GUI to manage an email alias per service. You could then disable email from a particular company at will. Anyone remember what this was?
You can do this with Gmail. Gmail will ignore anything after a '+' character in an email address. So let's say you have fakeperson@gmail.com, you can use:<p>fakeperson+facebook@gmail.com<p>to sign up for Facebook, and then create filters starting with "to:faceperson+facebook@gmail.com"