Best Plug In or Solution for Multiple User Registration?

Hello fellow WordPress fanatics…I am creating a new site but this one is different in that there should only be a couple public pages, one that gives a misson statement, another for links, etc.. but the rest of the site needs to be only accessible to registered users. What is the best way do set this up? I found all kinds of different plugins but have not found one that would work comprehensively?

I would like the users who come to the site fill in the administration form and then have access to the rest of the site. They need to all get individual users names and log ins…

Any ideas? I can make a form, have it email me and then we authenticate the info and create their logins etc manually but I would really like it to be automated.

As a side note: I have to be tight on security because its connected to a government office. Just by affiliation, but they still cannot have abuse.

A