Here's something which I know works well, and I consistently manage to forget to include, especially in my own marketing material. In The Sales Boosting Logic of the P.S. on Copyblogger, we're reminded that something added to the end of a message often gets more attention than almost anything else. It works in postal mail, in emails, and even on web pages.
PS: Bet you read this bit.
Published on 30 March 2010 
What do you think?