try www.ymlp.com . There is a free and professional version. The only differences i can tell, is that the professional doesn't have their advertising on your newsletters. The pro costs a little but i think it works out to about $1.50 - $2.00 a month.
Once you have signed up, you can access some code snippets to paste into your webpage....It's that simple. You can access your account with them online too. You have full access to your sign-up list and the management options are pretty good as well.
If you want to see how it works, go to my page(link at bottom) and sign up for the newsletter (you can unsubscribe afterwards if you want, the options are there). The email entry box and radio buttons are all created from their html code.
I use them and i believe retro64 uses them. I can happily recommend them, i've not had any problems at all.