I just found a free membership plugin for Wordpress, I wrote on the title that it's free but not cheap. It means that this plugin is totally free, but it has features that can compete with paid plugins.

I've tested several cheap plugin but none can compare to this plugin, it has been around for a while and I even has bookmarked it but I totally forgot about it until one forum members mentioned about it.

This plugin only supported paypal, this might be a draw back for some...