31. The Centauri Device - M. John Harrison

John Truck was to outward appearances just another lowlife spaceship captain. But he was also the last of the Centaurans - or at least, half of him was - which meant that he was the only person who could operate the Centauri Device, a sentient bomb which might hold the key to settling a vicious space war. M. John Harrison's classic novel turns the conventions of space opera on their head, and is written with the precision and brilliance for which is famed.

One of the poorer books in the SF Masterworks series. The story's interesting enough to keep the pages turning, but the characters are very shallow.

32. Dr. Bloodmoney - Philip K. Dick

Seven years after the day of the bombs, Point Reyes was luckier than most places. Its people were reasonably normal -- except for the girl with her twin brother growing inside her, and talking to her. Their barter economy was working. Their resident genius could fix almost anything that broke down But they didn't know they were harbouring the one man who almost everyone left alive wanted killed?

33. Non-Stop - Brian Aldiss

Curiosity was discouraged in the Greene tribe. Its members lived out their lives in cramped Quarters, hacking away at the encroaching ponics. As to where they were - that was forgotten. Roy Complain decides to find out. With the renegade priest Marapper, he moves into unmapped territory, where they make a series of discoveries which turn their universe upside-down...

An absolutely superb story, and one of my favourites from the SF Masterworks series. The ultimate conclusion is considered by some to be a let-down, but I was really impressed by it.

34. The Fountains of Paradise - Arthur C. Clarke

In the 22nd century visionary scientist Vannevar Morgan conceives the most grandiose engineering project of all time, and one which will revolutionize the future of humankind of space: a Space Elevator, 36,000 kilometres high, anchored to an equatorial island in the Indian Ocean.

Scientifically accurate and readable, but populated with a cast of typically shallow Clarke characters.

35. Pavane - Keith Roberts

1588: Queen Elizabeth is felled by an assassin's bullet. Within the week, the Spanish Armada had set sail, and its victory changed the course of history. 1968: England is still dominated by the Church of Rome. There are no telephones, no television, no nuclear power. AS Catholicism and the Inquisition tighten their grip, rebellion is growing.

36. Now Wait For Last Year - Philip K. Dick

First, Gino Molinari was assassinated by a political Rival. Then he died of a heart attack. But now he is back, younger and more vigorous than ever, giving Earth new hope of survival in the war against the alien reegs. But is this really Molinari, or a robant masquerading as Earth's overlord? Whatever the truth, only he can save the Solar System - if he can stay alive long enough, or at least not stay dead for too long.

37. Nova - Samuel R. Delany

The balance of galactic power in the 31st century revolves around Illyrion, the most precious energy source in the universe. Captain Lorq van Ray's varied and exotic crew know their mission is dangerous, but they have no idea of Lorq's secret obsession to gather Illyrion from an imploding star.

38. The First Men On The Moon - H. G. Wells

Published exactly 100 years ago, this is the only one of Wells's scientific romances to embrace space travel. Thanks to the discovery of an anti-gravity metal, Cavorite, two Victorian Englishmen travel to the moon, where they encounter the extraordinary underground world of the Selenites, insect-like aliens living in a rigidly organised hive society.

39. The City and the Stars - Arthur C. Clarke

Men had built cities before, but never such a city as Diaspar; for millennia its protective dome shutout the creeping decay and danger of the world outside. Once, it held powers that rules the stars. But then, as legend had it, The invaders came, driving humanity into this last refuge. It takes one man. A Unique to break through Diaspar's stifling inertia, to smash the legend and discover the true nature of the Invaders.

40. Blood Music - Greg Bear

Vergil Ulam's breakthrough in genetic engineering is considered too dangerous for further research. Rather than destroy his work, he injects himself with his creation and walks out of his lab, unaware of just quite how his actions will change the world. Bear's treatment of the traditional tale of scientific hubris is suspenseful and a compelling portrait of a new intelligence emerging amongst us and changing our world irrevocably.