Set your site to member only. All visitor will need to login to view site.

Simple SSL(HTTPS) Plugin.

This plugin redirects all not logged in users to a login page.

Ultimate content restrictions plugin with private page, private user groups,private conetnt and restrictions on menu,widgets,search,downloads based on user roles.

Disable the public site functionality, always prompt for a login before showing any content, make WordPress and intranet style site

Quick plugin to enable the setting of a site private. Includes options for with multi-site capabilities.