Having new members register with your WordPress blog to allow them to submit posts is a great way to get more content for free. This can also be a risk in itself so having a way to screen out risky people is best with plugins.

WP Members – This is a special plugin that only allows those who are registered with WordPress to be able to view your blog posts. This is only recommended if it is a website that is only used for blogging.

BuddyPress Registration – This is a great tool that allows people to register with your WordPress blog site but prevents them from doing more than changing their profile until an admin approves their account.

Register Plus – Allows you to have a custom login logo, send out invitations to the site and much more. It is a great tool for advanced user registration to prevent spammers and bots from getting into your site.

New User Approve – This is a handy plugin that allows registration requests to be handled for approval or denial by an admin before they have any access to WordPress elements.

Force Registration Field – This is an excellent tool to force new registering users to offer other fields such as usernames from other services and more. Registration is not possible without these fields present.