WordPress has emerged as not only a leading blogging platform but also a content management system for many Web publishers. Now there is a simple plugin available that will turn your blog into a paid membership site.
The WP-Membership plugin allows publishers to collect membership fees for WordPress blogs via PayPal, Authorize.net, and YourPay, with additional payment gateways in development. Membership fees can be collected via recurring payments, with multiple subscirption levels, various subscription lengths and pricing options. Free and paid trial options are also available, as are page-by-page options so that certain content can be free while other, "premium" content can be fee-based.
WP-Membership is available from Synergy Software Group for $29.97 for a single domain with lifetime free upgrades.