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.

mohanjith

Code Master

Helps you make the site available via https and http with no effort. Just install and activate 
and say good bye to SSL errors without forcing users to access via http or https only.
<h3>Notes & Credits</h3>
This plugin is written by <a href="http://mohanjith.com/" rel="nofollow ugc">S H Mohanjith</a>.
You should follow us on Twitter <a href="http://twitter.com/codemasteroy" rel="nofollow ugc">here</a>.

WordPress SSL

Have been using this plugin to resolve SSL errors for quite a while.  Has not failed and works just as advertised.  Ensures all links to resources are on the correct protocol.

Has worked well for a long period

Seamlessly map URLs to SSL if the site is accessed via SSL.

Protocol Enforcer vs WordPress SSL