Very easy to use and quick to setup. I have used it personally.
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.
BizRun - Manage HR and grow your business visually.
MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Sympa - Sympa is an open source (GNU GPL) mailing list management (MLM) software.
Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.
Worknice - Worknice is a performance management software that helps companies effectively manage their sales and customer-related business processes.