Fastmover

A simple drop down selection meta box on a post edit page will allow you to specify default, HTTP or HTTPS. Default will allow both HTTP and HTTPS protocols.

Protocol Enforcer

This plugin allows a user to specify a post to only be viewed over HTTP or HTTPS.

David Gregg

CCS-HTTPS is a simple plugin that allows you to identify which pages should have HTTPS enforced. All other pages will have HTTP enforced. 
This plug-in will not interfere with or override any of the built-in WordPress options related to forcing HTTPS for the login and admin pages.

CCS-HTTPS

A simple plugin that allows you to identify which pages should have HTTPS enforced. All other pages will have HTTP enforced.

Protocol Enforcer vs CCS-HTTPS