I prefer http://mailchimp.com/. If you have less than 2,000 people on your list and send out less than 12,000 emails a month, it's free. And, their RSS-to-email integration is sweet and I haven't seen others offer it. You can set up autoresponders. They are also in constant development and have lots of third party integration built in: twitter, facebook, highrise, eventbrite, etc.
I did a Constant Contact (and a few others) free trial a while ago and decided to go with MailChimp. Haven't thought about switching yet.