I like MailChimp fine. It does what it's supposed to do, and does it well. I have also used Mad Mimi and CampaignMonitor. I'm sticking with CM for now. It has

I like MailChimp fine. It does what it's supposed to do, and does it well. I have also used Mad Mimi and CampaignMonitor. I'm sticking with CM for now. It has more features and offers you the capability of setting up clients and allowing the to send email campaigns under your account, which can be cool. It also has excellent template features. All three are good, but this depends a lot on how much power you need, the number of emails you're going to send. The pricing structure varies a bit so I would look at that and figure out what works for you.