DSmidge

When WP is opened through HTTPS, all local absolute links in content are replaced from HTTP to HTTPS. 
Additional hosts can be specified through admin interface (like graph.facebook.com which works on HTTP and on HTTPS). 
Options HOME and SITEURL shuld be changed to HTTPS when enabling this plugin.

HTTP to HTTPS link changer by Eyga.net

When WP is opened through HTTPS, all local absolute links in content are replaced from HTTP to HTTPS.

WESLINK

CloudFlare Flexible SSL needs some tiny Modification to get not into a redirect loop. This Plugins makes your WordPress Site ready to use Cloudflare SSL and prevents the common SSL infinite loop Problem.
<a href="https://weslink.de/blog/" rel="nofollow ugc">WordPress and SSL </a>.

Cloudflare SSL by Weslink

we us it for our clients and like it :-)

Plugin to enable CloudFlare Flexible SSL for Wordpress and to prevent the Redirect Loop

HTTP to HTTPS link changer by Eyga.net vs Cloudflare SSL by Weslink