wp.insider

affmngr

This addon allows you to specify a MailChimp list name in the addon settings. When affiliates join your site, they get signed up to the specified MailChimp list automatically.
This addon requires the <a href="https://wordpress.org/plugins/affiliates-manager/" rel="ugc">Affiliates Manager Plugin</a>.
After you install this addon, go to the MailChimp settings interface and specify your API Key and the MailChimp list name.
Read the following page for step by step usage documentation: 
http://wpaffiliatemanager.com/signup-affiliates-mailchimp-list/

Affiliates Manager MailChimp Integration

An addon for the Affiliates Manager plugin to signup the affiliates to your MailChimp list

Dave Doolin

Aweber Super Simple is a plugin that will subscribe a user whenever 
he/she registers to your blog.
The AWeber Super Simple options page allows you to configure the plugin to: 
* Choose whether or not to display the optin checkbox. Users may register if optin isn’t shown, and will not added to autoresponder. 
* Choose a checked or unchecked default status for the optin checkbox on registration. 
* Provide a custom optin greeting message for visitors
This code base is at least once, possibly 3, 3 or more times removed from what was the original 
code base. Wherever or whenever the ultimate source, the base code is old in WordPress years. 
Current effort is to bring everything up to 2.8 coding standards before attempting any extensions.
<h3>Support</h3>
Initial functionality will be supported on a time-available basis.
Installation, configuration and further programming support may be 
available on a contract basis. Contact author with request.

Aweber Super Simple

AWeber Super Simple allows you to subscribe users to an AWeber autoresponder when they register on your blog. NOTE: ALPHA VERSION.  Be careful.

Affiliates Manager MailChimp Integration vs Aweber Super Simple