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.

Jason Coleman

Paid Memberships Pro

Add users and members to AWeber lists based on their membership level.
This plugin offers extended functionality for <a href="https://wordpress.org/plugins/paid-memberships-pro/" rel="ugc">membership websites using the Paid Memberships Pro plugin</a> available for free in the WordPress plugin repository.
With Paid Memberships Pro installed, you can specify unique lists for each membership level.
The settings page allows the site admin to specify which lists to assign for all users and members to plus additional features you may wish to adjust. The first step is to connect your website to AWeber using your account’s authorization code.

Paid Memberships Pro – AWeber Add On

Add users and members to AWeber lists based on their membership level.

Aweber Super Simple vs Paid Memberships Pro – AWeber Add On