In spite of following different ways, all email newsletters have to automate the list management and find an easy method to administer it. If you surf the Internet, you can find a number of free newsletters or mailing list providers. They normally use a web-based administration area and include Your Mailing List Provider, ListPower, Notify List.com and ListApp. You may prefer a solution where the list is hosted and managed by a small business specialist like Constant Contact. Monthly rates go up with the number of subscribers, though lists of contacts not exceeding 50 are free.
If you are happy with web page design you should be able to install and run a PHP script. You can try MyMail, a free PHP script that works very well. You can find plenty of other scripts in PHP and other languages at HotScripts.
Commercial programs such as eNewsletter Pro, Post Cast and MailWorks Pro can also do the job for you. They either run on the web server or on your desktop. You should not just keep adding people to your list without their permission. This is called spam, which is a big taboo capable of driving your customers away.
As there are some problems with sending HTML newsletters as email, it is better to provide your readers with the ability to choose what format they prefer. This needs a more powerful program to manage the list, and you might need to format a plain text and HTML version.