Aw Guo

This plugin will allow users to digg / bury every thread of your comments, thus find out the most valuable comments as well as the human-spammers.

WordPress Comment Digg

Digg or bury your comments and generate a percentage bar in your comment boxes.

goldenapples

This plugin aims to support community link-sharing, social bookmarking, and discussion of links in the WordPress environment.
This is still at an early stage of what I hope will be a much more ambitious project. If you want to try this out, please give me feedback.
I will guarantee backwards compatibility with all data saved by the plugin, so it should be safe to install and activate, and as I add features, your existing posts and links will work with them just fine.
See the plugin’s <a href="https://github.com/goldenapples/recommended-links/wiki" rel="nofollow ugc">wiki page on github</a> for more up-to-date documentation (its hard to keep documentation updated in multiple places).

WordPress Comment Digg vs Recommended Links for WordPress