Mailchimp makes pretty newsletters and it's free, so it's hard to go wrong. I've only sent out a handful of newsletters, and I learn something new you can do every time, so I'd say there is a bit of a learning curve to learn all you can get out of it.
And, of course, they have a paid version that let's you do even more. But right now, the free one is working fine for me.
I do seem to get traffic from the newsletters I send, so I need to get better about it.
