s2Member® (Membership w/ PayPal®). Powerful (free) membership capabilities. Protect members only content. The s2Member Framework (free) integrates w/ PayPal® (very easy), and fully supports recurring billing. s2Member supports custom Pages for registration (including Custom Registration Fields), account access, and a lot more. s2Member is now compatible with Multisite Networking too, and even with BuddyPress and bbPress.