Newsletter Professional is a free wordpress plugin by martinszigkos that lets you collect subscribers on your blog with a single or double opt-in subscription process. Create and send professional HTML newsletters to your users and subscribers within seconds.
Features:
Create and manage your newsletters.
Professional designed templates.
Track statistics of subscribers.
Display it as a widget on your site easy.
Ability to modify subscription using a panel.
Download: http://wordpress.org/extend/plugins/newsletter-professional/