I've been using aWeber for about five years. It's like Constant Contact, but much better. It's a double opt-in email and contact management system. For all of my sites, I've set up an aWeber popup for first-time visitors (yes it knows if you've been there before), asking you to join our email newsletter and explaining all the advantages. Once they've joined, they'll receive an email to confirm. aWeber has much higher delivery rates for emails due to their double opt-in system. I use if for distribution of my monthly email newsletter as well as periodic events updates from our hyperlocal blogs. It's not a cheap system, but very robust.