I have just made a new plugin named Social It. The plugin is inspired from the wonderful plugin SexyBookmarks created by Josh & Norman for WordPress (and is almost the same like that)
It automatically inserts itself below the first post of the topic, but you can insert it anywhere on the forums. It will automatically fetch the appropiate feed link, description, etc.
It supports a variety of short URL sites to shorten links, I will improve this feature in the upcoming releases, like managing the links within the plugin itself, etc.
Please report any bugs you face, or request new features.
Here is the link for the plugin: