On the Web Development Blog there's a recent post looking at the integration of the MailChimp mailing list service with your current application for list management.

MailChimp is a great mailing list provider with a great control panel and many useful features like: campaign management, statistics, responders and complete set of List management tools. They offer also an small code snippet to place a subscription form on your website. This form powered by jQuery is good enough for most common cases, but what if you like to combine your newsletter subscription with a standard function like contact or registration form?

They show you how to create the front end - a HTML form pointing to your own PHP script - and the PHP code to make a cURL request over to the MailChimp servers to subscribe the given email address to your list.