Here is a Flickr set by French illustrator Stéphane Massa-Bidal (Rétrofuturs), who has designed a bunch of really incredible covers for nonexistent books about major web services. My favorite is the one he's designed for professional networking site LinkedIn, and its tagline: "A friend is one who has the same enemies as you have." (A quote which is widely attributed to Abraham Lincoln, although I can't figure out from where, so maybe it's apocryphal.)
I don't know if they're designed to look like a specific series, but they remind me a whole lot of Penguin's paperbacks from the 1960s.
(Found via The Daily What via Design You Trust)