The s2Member® Framework (free) integrates with PayPal Website Payments Standard (also free). Sell "Buy Now" or Membership access to your site. Restrict access to Roles, Capabilities, Posts, Pages, or anything else in WordPress.
Protect your WordPress Posts, Pages, Tags, Categories, URIs, BuddyPress/bbPress, and even portions of content within Posts, Pages, themes, plugins. Easily configurable & highly extensible. You can even protect downloadable files and streaming audio/video. Store files locally, or use s2Member's integration with Amazon® S3/CloudFront. More Info »
s2Member is powered almost entirely by WordPress shortcodes, making complex integrations quick & easy. Sell recurring (or non-recurring) subscriptions with lots of flexibility. Or sell "Buy Now" access in various ways. You can also sell specific Posts/Pages, sell access to file downloads, or sell Custom Capabilities that provide highly configurable access to specific portions of your content.