I very much recommend this one!
I tried quite a number of plugins for subscribing, but most of them lack the possibility to send mails as well. This one does that, and it's really easy (some basic HTML knowledge helps) to setup.
I work profesionally within the field of emailmarketing. All basic functionality for collecting e-mailaddresses (customizable forms, editing user profiles, unsubscribe), setting up a mailing (using either the given templates or custom made), sending it to specified target groups (including very important pretesting possibilities), yes even some statistics reports; it's all in there.
This chap has really done a tremendous job!