WordPress Plugin: WP OptIn
If you are looking to grow your e-mail list, stop using pop-ups, and start getting your commenters subscribed.
WP OptIn is a WordPress plugin that allows your commenters to subscribe to your email newsletter or auto-responder simply by checking a box automatically placed in your comment forms. The plugin integrates with Aweber, ConstantContact, or MailChimp to subscribe commenters without an extra subscription step.
A paid WordPress plugin, WP OptIn is $29, but for the affiliate marketing guru looking to expand their e-mail subscription list, this could be a fast, and effective way to do so. If you are interested, check out the dedicated site they have for the plugin at WPOptin.com.