I'm releasing another free Joomla/Mambo module; this one allows you to put an email subscription form on each page of your website. The subscription list works with Constant Contact, an affordable email service provider. You can sign up now for free, and if your list is under 100 subscribers the service is free. http://www.justin-cook.com/wp/2006/04/17/build-your-email-subscriber-list-on-your-joomlamambo-site/
This is merely a 'signup' module, if you're using 3rd party Constant Contact service for email campaigns