One plugin which could be very useful in a WordPress installation is a Newsletter plugin. For me the essential features of such a plugin would be to enable me to import and export contacts, then be able to send them an email newsletter all at once.

In order of preference, my favourite Newsletter plugins for WordPress are:

• MailPress (frequently updated, great interface, features and a number of add-ons)
• Pluginbuddy (recently released, seems very promising)
• MeeNews (development seems to have stalled on this, although it does have some impressive tracking features, I don’t particularly like the interface)
• Semiologic’s Mailing List Plugin ($49, many users report unresponsive support, has good interface, features, and statistics)
• Newsletter by Satollo (frequently updated, good feature-set, needs upgrading to a paid system for more advanced features)

Alternatively one can use the Open Source PHPList system together with the WordPress integration plugin

If using Campaign Monitor (not free) there is a plugin which integrates WordPress to this system.

Lorelle’s post also has some systems reviewed and is well-worth reading, although it’s a bit old now.