BriceRhodes

You can try the S2members plugin I use s2members for my membership site and it has a ton of features including allowing people to register in order to post articles, although that is more of a built-in wordpress feature.

Your Login/Registration Form (already built-in)

s2Member uses the existing WordPress® Login/Registration system. This is the same Login/Registration Form that you use to access your WP® Dashboard. However, with s2Member installed, your Login/Registration Forms can be customized (i.e. re-branded). See: s2Member -› General Options -› Login/Registration Design. You can make the default Login/Registration Forms match your WordPress® theme design; by changing the background color/image, your logo image, add Custom Fields, and more!

Since s2Member uses the default Login/Registration system for WordPress®, s2Member is also compatible with themes and other plugins (such as BuddyPress). If your theme has a login form built-in already, chances are, it’s perfectly compatible with s2Member. There are also many plugins available that are designed to place login forms into your Sidebar; and many of those are also compatible with s2Member’s integration. If you have any trouble, please check the s2Member Forums for assistance.