
Ever wonder what it would be like to live in cities that flew around in space, like small planets? This book takes you there.
One that only the older set may know is Cities in Flight by James Blish (technically a trilogy but primarily sold as the single combined novel).
Getting past the first chapter of Pandoras Star is well worth it - Morninglightmountain is one of the most original, minblowingly awesome all time alien baddies, and the trepidation and sense of impending doom in that book and its's sequel Judas Unchained are superb. Would also recommend the Void Trilogy by Peter F Hamilton too - strong mix of scifi and an alternate fantasy world.
Missing in my view would be: Greg Bear - Eon (as people have mentioned, but also: M John Harrison - Light James Blish - Cities in Flight Battlefield Earth (awesome book, hopeless film) Brave New World for my ultimate "classic"
While trying to find an online reference for this, apparently in the last Ringworld novel they hook a hyperdrive up to this, making it the largest "ship" I know. (I use "I know" advisedly... I'm sure somebody somewhere has turned a multiverse into some sort of ship for some reason or other.)
In the Cities in Flight series by James Blish, the planet "He" gets about quite well, though that is dwarfed in every measurement by the Ringworld.
