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.

blackc2004

This plugin will make sure that all elements on a page are SSL if the page is being accessed via HTTPS. For this to happen you must have used correct programming practices and use siteurl, wpurl, url etc where all the locations are supposed to be.
Some plugins do not correctly use this, I have already notified a few of them, but you may find some other issues, if you do, please contact me and I will research and attempt to notify the developers of the other plugins.

HTTPS for WordPress

Check to see if SSL is used. This will update any template functions which require SSL to be used.

Protocol Enforcer vs HTTPS for WordPress