Programming for Marketers

Lesson 3: Tools and Scripts to Capture More Emails and Engage Your Signups

1.3 Getting Email Addresses When People are About to Leave

You’d be amazed at how many people you can convert at the last second by installing a simple exit script. The idea of this is simple, when your page detects that someone is moving their mouse quickly towards the “X” in the top, it brings up a pop-up encouraging them to sign up again.
Exit Monitor will help you get set up on custom sites, and wBounce is a great plugin for WordPress that will do the same thing.
 http://www.programmingformarketers.com/more-email-signups/