WP PHPList (phplist-form-integration) free WordPress plugin

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 <!--phplist form--> on any page on your blog. It’s easy and fast and does not require any
further template modifications in PHPList or WordPress.

Demo

See an example of this plugin at Wedding Cake Newsletter Demo