atonyk

This plugin adds the ‘Like’ button and ‘Who Likes’ list to:
<ul>
<li>WordPress posts and comments</li>
<li>BuddyPress activities and comments</li>
<li>BBPress posts</li>
</ul>
It allows for registered users to like the items. And it shows for both registered and unregistered users the existing likes.
The components to show the likes to can be configured on the settings page. For example, the likes can be disabled for WordPress comments.
Likes are saved in the internal WordPress and BuddyPress meta tables. No separate tables are created.
The plugin cleans all its data on uninstallation (but not on deactivation).
You can contribute on – <a href="https://github.com/ansnap/like-and-who-likes" rel="nofollow ugc">https://github.com/ansnap/like-and-who-likes</a>

Like And Who Likes

Adds the 'Like' button and 'Who Likes' list for WordPress, BuddyPress and BBPress.

Riccardo Conte

This plugin implements a “like/dislike” rating system for comments. In the setting page you can choose a “compact / splitted” mode that show ratings like sum or separately.

Zaki Like Dislike Comments

This plugin implements a "like/dislike" rating system for comments

Like And Who Likes vs Zaki Like Dislike Comments