WP PHPList Comment Subscriber is a WordPress plugin that gives users the option to subscribe to your PHPList newsletter when adding comments to your blog. It requires PHPLIST newsletter manager to work.
It adds a checkbox with customizable text which gives the user the option of automatically being subscribed to your PHPLIST managed newsletter. This integration provides another channel for capturing well-targeted newsletter opt-ins.
phplist is an open source email campaign manager. phplist is free to download, install and use, and is easy to integrate with any website. More info: www.phplist.com
Demo: http://blog.pinkcakebox.com/yorkie-rehearsal-cake-2010-06-26.htm#comments/
Download and info: http://wordpress.org/extend/plugins/phplist-comment-subscriber/