Feedburner Form is a WordPress plugin by Dianakc, that allows you insert Feedburner subscription forms in widgetized areas of you site. By using this form, you allow visitors to subscribe to your feed and receive an e-mail sent by Feedburner, everytime you publish content. Also, you don’t have to worry about manage subscriptions: the visitors can subscribe and unscribe themselves through Feedburner service.
Download and info: http://wordpress.org/extend/plugins/feedburner-form/