Knews is a WordPress plugin that aims to create and send fresh newsletter. it has a What You See Is What You Get (WYSIWYG) editor which can help design an interface in less than a few minutes. It comes with other features like multi-language support, better user administrator, and automated newsletter creation. This plugin is available for free and it can be installed just like any other WordPress plugin.
Knews is a plugin available for free similar to MailChimp, and Aweber. It has more features than the two mentioned plugins but the difference is fairly limited to your needs in a plugin.
Read the rest of the review here: http://wpnuggets.com/wp-plugin-review/knews/