If you want newsletter plugins for WordPress, you can find a whole bunch of them, with many different levels of quality and features.
One new plugin released recently is e-Newsletter by WPMU, which are well know for the quality and range of their WordPress plugins.
e-Newsletter has some great features, including professionally designed newsletter templates, unlimited groups and subscribers, tracking, and more.
Pretty cool. If you are looking for a way to send newsletters from WordPress, you should check it out at WPMU.
Pros: Easy to install and use, nice features, good support.
Cons: Not free. It uses your own host to send the e-mails, so the deliverability might be inferior to professional services. Plus your own host might have limits on total e-mails per month or hour. But that is a problem shared by pretty much all newsletter plugins for WordPress, or any self hosted solution.
Because of those reasons I personally use MailChimp myself.