Drupal is our suggestion for this because of a number of factors: 1) It is built on a community focus, that is, with multiple levels of permission for user roles, 2) it is able to be extended to have many different types of content, e.g. a single "paid user" might be able to create: blogs, images, coupons, or the like 3) it is highly supported by a wide developer community, 4) it has many different member solutions built-in such as e-commerce, marketplace functionality, private messaging, flagging, five-star rating, wishlists, and groups to handle members-only content

I've produced multiple member sites on Drupal and written about it here: http://10kwebdesign.com/10kblog/step-step-setting-membership-community-site-using-drupal -- Drupal is currently moving into version 8 so now is a great time to start planning what you want the membership community to do and what kind of features you want to allow.