This is a simple extension that utilizes the Mailchimp API to subscribe customers to a specified Mailchimp List on sucessfull checkout. The Mailchimp API key and List ID are defined from System -> Configuration -> Developmint Settings.
It uses an exiting implementation of the MailChimp API found here: http://apidocs.mailchimp.com/api/downloads/#php
#Please Note
A checkbox field with the name 'newsletter-signup' needs to be added to the checkout process for this extension to work.