Here's a cute picture of the Peanuts gang depicted as characters from Alan Moore's Watchmen, which I found on a German site called Nerdcore.
While I love the sentiment, I think the creator got the characters a bit wrong, to wit:
Charlie Brown is definitely Nite-Owl. Nite-Owl is an every man, who does his best despite knowing that most of his efforts are ultimately doomed to failure.
I like Schroeder as Ozymandias. They look sort of similar, and both clearly have some special gifts.
Pig Pen has got to be Rorschach. A traumatic childhood would explain a lot about why PigPen is such a mess.
I think Linus is Dr. Manhattan. Linus is sort of the moral center that the Peanuts world revolves around. Although Manhattan has his own unique morality, both he and Manhattan are Jesus-like figures in their respective universes.
By extension this would make Sally the Silk Spectre, since their relationship is a key element of both universes.
Finally I think Lucy is the Comedian. She sees the world as it is and finds it both wanting and entertaining at once, as she pulls the football away every time.