Restrict Content Pro is a membership plugin for WordPress based websites. It will allow you to secure and sell content and includes a number of add-ons to cover most requirements.
Restrict Content Pro is a serious plugin to consider using for your membership website. Sadly many basic features are only available in the $249 per year package. Now if you are a web developer, and are going to use RCP on many websites, this cost is not that big of a deal, but if you just need it to power 1 website, it may be expensive.
One of the interesting things is that this is just about the only reliable membership plugin for WordPress that still offers a lifetime plan.