MailChimp makes it easy to design and send beautiful emails, manage your subscribers and track your campaign's performance. We take fancy-schmancy tools like segmentation, a/b testing and ROI tracking, and we turn them into something anyone can use.
MailChimp is an *awesome* email marketing tool. It really has it all: easy to use blog-like interface for creating newsletters, a simple, step-by-step guide to get your newsletters sent, and great analytics to understand what people are clicking in your email (the clickmap overlayed on your newsletter is so useful!).
I use MailChimp for a side project I run (GreenhornConnect.com) and it makes my life so easy and allows me to invest very little time with massive returns. I highly recommend!