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.

mitchbartlett

Fixes images that load under HTTP instead of HTTPS on a web page that is protected via SSL.

HTTPS Image Fixer

Fixes insecure content messages that appear when loading images on an SSL secured website.

HTTP to HTTPS link changer by Eyga.net vs HTTPS Image Fixer