I agree that autoresponders are a very powerful (and inexpensive) marketing tool. Not to mention a great way to automate responding to inquiries, etc.
I personally haven't used any of the email marketing/autoresponder services. A long-time internet marketer once gave me the advice to always handle those services in-house -- that way you never have to depend on someone else's servers, flaky customer service, etc. I've been doing so successfully for almost four years now.
For a long time I used (and recommended) ListMail Pro (http://www.listmailpro.com
). Dean (the developer) is a good guy and at a one-time cost under $200, it's a great deal. However, I recently moved up to SendStudio (http://www.interspire.com
); at just $239, it's still a great value for what you get -- unlimited lists, unlimited autoresponders, personalizable emails, great statistics and easy-to-build subscribe, change, and unsubscribe forms. The last two are what made me move from ListMail to SendStudio, although ListMail may have added features since then. Another bonus with SS is the built-in wysiwyg editor for html emails -- sweet! (and easy for my VA to use
I'm not associated with either of these products. However, I'm happy to answer questions about the features I've used and how well they work -- including features like segmenting my list, selective sending, link tracking, etc.