s2Member is a full-featured membership management system for WordPress®. It provides a very tight integration with PayPal® Subscriptions, and fully supports recurring billing with the ability to track affiliate commissions on a recurring basis.
s2Member supports up to 4 different levels of membership with custom labels. It supports custom Pages for signup, account access, and many others. It also supports the ability to protect certain Pages, certain Posts, certain Categories/Tags, certain parts of content, and even includes advanced documentation on how to utilize the PHP runtime constants provided by the s2Member API. s2Member also supports protected file downloads with limitations on the how many files each user ( or each level ) can download in a given period of time.