Login Back-end site

I am currently redesigning a site for a company I work for and we would like to have a log in section for members to be able to enter their information and be able to access some additional content that isn’t made available to the public site. i was wondering if there is any one good way to do this and if there are some plugins to make things easier. My initial thought was to create a link to a subdomain site that would have a login page to be able to access the subdomain. If anyone has anything better that would work, I would really like to know more. Additionally any advice on plugins to use would be extremely helpful as well.