Magento Newsletter Integration

MailChimp:
http://www.magentocommerce.com/magento-connect/mage-monkey-mailchimp-integration-4865.html

Constant Contact:
http://www.magentocommerce.com/magento-connect/constant-contact.html
http://www.freelunchlabs.com/store/constant-contact-and-magento-sync.html

IContact:
http://www.magecoders.com/index.php/magento-extensions/icontact-sync.html
http://www.magentocommerce.com/magento-connect/icontact-sync-9752.html