This is a pretty cool experiment which shows a rat helping a compatriot as well as sharing chocolate treats with them -- and I think we all know that sharing your chocolate is a true sign of friendship!
Another recent study on rat cognition, learning and dealing with ambiguous situations. Though the article opens by saying rats behave "as if they're rational creatures" [emphasis mine]. Ah well. Can't win everyone over to the wonder of rats right away, I guess. ;)
Just remember, someday you may meet rat-powered robots, so their altruism and rationality is important to you! (insert evil laugh)