Flight of Manhattan
Fun with MapQuest and Google Maps.
First it was Bill Renken's Errant Isle of Manhattan, on Radical Cartography: "What would happen if Manhattan itself decided to take a tour of the oceans, stopping at other cities to refuel and have a good time."
First stop: Chicago
Jason Kottke speculates on a visit to San Francisco
Seth Holladay takes the island to Boston
However, the first thing I thought of, after viewing these fantastical maps, was the series of science fiction books by James Blish; Cities in Flight. Centuries into the future, the invention of massive antigravity devices allow entire cities, including New York, to get up and leave the planet. These "Okies", as they come to be known, struggle to get by as they offer their services to less industrialized planets.
UPDATE 6/10: Just came across this entry in the Worth1000.com B2B: Miniature Worlds contest: Colony City By funkwood