Ripple

This plugin brings Related post slider to the WordPress blog post.

100% free related posts with six layouts, a block, editorial picks and local reports. No premium version, account or API key.

Display a list of related entries on your site based on an unique, self-learning, socialsemantic network analysis algorithm.

Adds post pagination, related content, author info, social sharing buttons, post meta, text, image and banner after posts content.

A WordPress plugin that adds related posts by category to the bottom of your single post template.

Like trackbacks, but not -- this plugin searches and displays content related to your CONTENT, not just posts that link to yours.