jesseheap

This lightweight plugin for WordPress 2.0 or greater gives you the ability to easily allow users to subscribe 
to your newsletter or RSS blog feed from any page on your blog. Simply install the plug-in, configure your settings, 
and embed the comment <code></code> on any page on your blog. It’s easy and fast and does not require any 
further template modifications in PHPList or WordPress.
<h3>Demo</h3>
See an example of this plugin at <a href="http://blog.pinkcakebox.com/wordpress-plugin-demo/" title="Wedding Gallery" rel="nofollow ugc">Wedding Cake Newsletter Demo</a>

WP PHPList

This lightweight plugin for Wordpress 2.0 or greater gives you the ability to easily allow users to subscribe

vinzzb

This plugin imports forms from you PhpList host into wordpress. 
Your subscription forms can be used anywhere in wordpress using shortcodes. 
Custom user attributes defined in phplist are also taken into account. 
The plugin uses async calls (ajax) for registrations. You can fully customize the respone on success or failures.
NOTE: This plugin will only work with self hosted PhpList environments. It does not work with phplist.com accounts.
<a href="http://coderisk.com/wp/plugin/phpls/RIPS-6cAWMzmXxg" rel="nofollow ugc"></a>

PhpList Subber

Integrate your PhpList subscription forms in Wordpress, including user attributes in phpList.

WP PHPList vs PhpList Subber