In 1988, as part of a print advertising campaign, Volkswagen asked many thinkers, including author Kurt Vonnegut, to write letters to the people of 2088. Vonnegut's words of advice: Nature is out to kill us all and instead of being overly optimistic, we should submit to its terms of surrender.
Even the greats get Writer's Block. But when you're Theodore Sturgeon, you can get some advice directly from Robert A. Heinlein.
You may have recently encountered Carl Sagan's 1954 reading list out in the internet. But the Library of Congress has posted some much more interesting papers from the scientist, novelist and all around fascinating guy: a draft of the 1995 letter he sent to Warner Brothers about the adaptation of Contact.
The Muppets' Dr. Bunsen Honeydew considers himself the foremost pioneer in crazy scientific endeavors. So when NASA landed the Rovers Spirit and Opportunity on Mars, Bunsen was understandably miffed. Still he was classy enough to send a letter of congratulations to the team, along with his offer of help.