Didn't expected to find a listing of aMember here, but as a licensed user since his early days (2003) and used it with more than 10 official integration plugins, I can say that aMember is by far the best script to handle memberships, protected areas etc. Almost impossible to find a payment gateway that is not supporting, or integration plugin for your favorite CMS. Once I was operating a website with 5 different script and I was using aMember as central script to handle memberships and single sign-in. Coming to support, can't find which is the right word to use. Excellent? Superior? Really don't know. The best of the best friendly support not only in ticketing system but also in their forums.
