The top two in the industry are Aweber and GetResponse. I think you probably couldn't go wrong by choosing either one of those for your auto-responder needs. Before choosing one, I did a fair amount of research. Ultimately, I decided to go with Getresponse and have been very happy with them. Aweber and GetResponse are actually quite similar as far as features offered. GetResponse is somewhat cheaper. You can start out with their free version and then transfer to a paid subscription.

With GetResponse, you have the ability to set up an unlimited number of campaigns. This is ideal if you have websites in a number of different niches. You can set up different auto-responders for different sites. I also like their spam check system. This feature allows you to design your emails so that spam filters will not think they are receiving spam and send my emails to a bulk file.

I also investigated the autoresponders that reside on your own computer. It is nice in that it gives you complete control over the entire process. These auto-responders were significantly cheaper (some of them were free). However, I decided against it after investigating the laws governing spam. There are some very strict laws in effect regarding spam that carry significant penalties. GetResponse's procedures keep me out of trouble in that regard and that was very important to me.

GetResponse currently allows unlimited follow-up messages. As time goes on, you will come to realize that is a very important feature. It also provides 19 alternative domain names to receive messages.

It has a spam-check feature to avoid detection by other ISP's spam filters, and provides a list builder service to help you build your opt-in list (at a cost).

The current price starts at $17.95 per month for a basic account, with a refund period of 30 days. You can get it even cheaper if you sign up for a longer period. Another great feature is the fact that they provide toll-free phone support. Phone support is very important in the event that your computer (or theirs) goes down.

If you are looking for an autoresponder, I can recommend GetResponse very highly.