Does anyone know of a plugin, free or paid, that adds content automatically to your articles? I was thinking of using a plugin to add news from other sites, Twitter posts, Facebook comments and the like to posts automatically to make them more dynamic. Does anyone know if such a plugin exists? I searched the Wordpress Plugin repository up and down but could not really find a suitable one.

Free ? No. The free one, can only add content from feed. However wp-robot can give you what you are looking for. PM me if you need more help.

wprobot
wpturbo
blogsense
rssposter pro
autoblogged
cyberseo
autoblog samurai
get article pro

And there are also some free versions like wp-o-matic.

That's why I love this forum so much. So many helpful people around. Thanks guys, I will spend the rest of the day researching those plugins