I had a site that I needed to keep completely private: only the login and registration pages were to be visible to the public, and only registered members were allowed to see the content. I wanted a way to fully control who registered for the site, short of my registering each member myself. Register Plus Redux (RPR) by RadioK let me do just that. This plugin is a fork of Register Plus, which hasn’t been updated since 2008. Here are some of the features:

• Invitation codes. These are short codes that you can give to an individual or group of people that they will use to register for the site. An extra layer of security, so that you can be sure that the email address behind a registration actually belongs to someone in particular. Also, without an invitation code, the registration can’t be completed, so this avoids dealing with unwanted registrations.
• Uses email as username (so people don’t need to remember their username).
• Custom profile fields; for example, you could have a field named “Gender” and ask the members to specify M or F.
• Custom registration email sent to new members, which can include fields such as the username.
• Ability to show a disclaimer, privacy policy and/or license agreement during registration.
• Users can pick their passwords themselves (no auto-generation).

Some of the Admin settings

Another great thing about this plugin: the author is very open to suggestions and bug fixes. See that 2nd item on the list (emails as username)? That’s mine. Some of my members do not visit the site very often and they kept forgetting their usernames, so I had told them to always use their email addresses as their username. RPR lets me hide the “Username” field on the registration page, and uses the email address as the username automatically. Nifty!

If you want better control over user registrations, this plugin is definitely for you.