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.

Dwenaus

BuddyPress 1.6 compatible. Users can rate forum posts in BuddyPress. Good posts are highlighted and poor posts diminished. Highlighted karma points shown for each user. Only works with forums for groups; not compatible with site wide forums.
Features & Options: 
* Post rating and responses via ajax. 
* Posts can only be rated once: thumbs up or thumbs down. This can be replaced with ‘like’ and ‘dislike’. Super-admins can rate a post as much as they want, however group admins can only rate once. 
* Good posts are highlighted light yellow (default +10), great posts are highlighted bright yellow (default +25), poor posts become slightly opaque (default -3), and very poor posts have their content hidden and viewable via an ajax link. (default -6). 
* Karma points are given to each user based on their posting history. Karma points can be based on total accumulated ratings (good for quiet sites), average post rating (good for very busy sites) or a balance of the two (good for medium traffic sites). The default is the later. 
* User Karma points are highlighted depending on number of karma points. There are 5 levels (based on natural log). Default, above 7p, above 19p, above 51p, and above 138p. The scale goes from grey to bright yellow. These values can be edited in bp-rate-forum-posts.php 
* Topic ratings are shown in group and forum listings view using the rating of the initial post. 
* Only logged-in users can rate posts. 
* No new database tables are created. 
* Post Karma shows on Member view 
* There is an admin screen to change karma levels, post highligting and diminishing values, and karma calculation method 
* No post rating when the topic is closed (except admin)
Thanks to Intense Debate for their thumb graphics and good layout.

BuddyPress Rate Forum Posts

Users can rate group forum posts in BuddyPress. Good posts are highlighted and poor posts diminished. Highlighted karma points shown for each user.

Like And Who Likes vs BuddyPress Rate Forum Posts