Color Scheme Every Theme lets you change the entire color scheme of the current theme via the theme customizer.
Force ReAuthentication allows a site administrator to log out a user remotely.
Branded Login Screen allows you to customize your login screen.
Markdown on Save Improved processes your post with Markdown unless you tell it not to.
SyntaxHighlighter Evolved allows you to easily post syntax-highlighted code to your site without having to escape the code or anything.
Yet Another Related Posts Plugin displays a list of related entries on your site and feeds based on a unique algorithm.