PHP List is very simple to setup with great documentation. It's also easy for customers (non-technical) if they want help setting up their lists or need support when things go wrong! The customer service can be slow at times but I guess that comes from working remotely in different time zones so it takes me longer than normal business hours. Their pricing isn't too bad either compared against other providers out there - you get what your paying for :) We use this system as an automated mailing tool which allows us send newsletters via our website without having staff members manually adding each person who has subscribed by hand into Outlook/Exchange etc every month.