Earthman, Come Home
by James Blish (1955)

The first Cities in Flight novel published is actually third in line when it comes to internal chronology. Flying cities powered by antigravity devices give the Earth police all sorts of excuses to impose 'order' on the spaceways. John Amalfi has been mayor of NYC for almost 500 years - and life on an 'Okie' city isn't getting any easier. Available as an omnibus.

Non-Stop [vt Starship]
by Brian Aldiss (1958)

Currently enjoying a renaissance in popularity, Non-Stop is the story of the Greene tribe that unquestioningly lives in tunnels surrounded by ponic vegetation. Unhappy with the general cultural acceptance of the situation, Roy Complain sets out with a group to push some boundaries and solve the really big question.

Ringworld
by Larry Niven (1970)

A crew sets out to explore the huge 'Ringworld' artificial object. The foursome survive encounters with the local inhabitants ("nothing but savagery"), who are seemingly very human. The apex of the Tales of Known Space sequence, Niven's hard sci-fi may be far too technical and a bit short on entertainment value for some tastes.

Rendezvous With Rama
by Arthur C Clarke (1973)

Captain Cook-obsessed commander leads crew in exploration of interior of huge cylindrical alien artefact on near-sun trajectory. No-one knows who built it or why it is here. The allusion to Cook hints at the fundamental premise on offer which celebrates the pure joy of exploration. The book won a swag of awards including a Nebula and Hugo, in the process remaining one of Clarke's most popular.

Lucifer's Hammer
by Larry Niven & Jerry Pournelle (1977)

Popular novel describing social upheaval in days leading up to a collision with a huge comet and the struggles faced by those who survived. There is a nice bit of US/USSR cooperation and, as usual, Niven's science is pretty much on target. Some may find the book a bit too formulaic in comparison to the superb Mote In God's Eye.

Titan
by John Varley (1979)

A NASA expedition sent to explore Saturn's largest moon finds that it is actually a sentient alien artefact called Gaea. It eats them and, once inside, they find it is populated with an array of characters and beings from Earth's mythology as seen on TV. First book in the popular Gaean Trilogy, although most critics prefer other JV works.

Eon
by Greg Bear (1985)

Remarkable hard sci-fi tale about a starship asteroid floating above Earth that triggers a global war. The 'Stone' turns out to be the product of humans from a parallel universe. Bear's explanation of the science behind the Stone's inner-dimensions being larger that its outer (e.g. the Dr Who TARDIS) is a joy to behold. Highly recommended.

Rama Revealed
by Arthur C Clarke & Gentry Lee (1994)

Hailed as everything from the biggest dud in modern sci-fi to the best of Clarke's Rama series, anyone thinking of investing in this book should do their homework first. While heading towards the climax of its journey, some humans on the massive spaceship Rama III encounter the technologically advanced octospiders. Pretty ho hum.