Are penguins solitary or social?

  I have been wondering if penguins are solitary or social but i just can't seem to find the answer.
They're very social.

see

http://science.jrank.org/pages/5081/Peng ...

http://www.seaworld.org/animal-info/info ... (though the first point is a bit off. The Yellow-eyed and Fiordland penguins aren't colony breeders).
I saw somewhere where hundreds of penguins make a huddle to keep warm, so warm to the point that if the penguin in the middle doesn't switch out it can die from overheating.
Social