Foundation Trilogy
by Isaac Asimov (1951-53)

Much-loved series tracing the decline and fall of a galactic empire. Psychohistorian Hari Seldon, however, makes contingency plans - with art, science and technology eventually saving the day. Asimov's scientific background shows in Foundation's frequent intellectual discourse. Won a retrospective Hugo as all-time best series.

The Rediscovery of Man
by Cordwainer Smith (1975)

Posthumous collection by political scientist and military adviser Paul Linebarger, published under his now-famous pseudonym. These are the best of his Instrumentality stories about a universe ruled by omnipotent lords - most of which are contained in original volumes You Will Never Be the Same (1963) and Space Lords (1965).

The Mote in God's Eye
by Niven & Pournelle (1975)

The first of several successful collaborations set in Pournelle's CoDominium future. A fully-blown interstellar human empire - complete with royalty and a powerful military sub-class - have an unexpectedly dangerous encounter with the alien Moties. Pournelle's narrative skill and Niven's technical acumen are the perfect mix. All-time favourite.

Downbelow Station
by C J Cherryh (1981)

In the 1980s Cherryh emerged as the best practitioner of modern space opera with a series of exciting novels set in her Union-Alliance future history. Downbelow Station sees the balance of power between the deteriorating Earth Alliance, aggressive space-based Union and the merchant-freighter class begin to unravel. Cherryh's best, although others are good too.

Startide Rising
by David Brin (1983)

With his Uplift saga physicist Brin wrote some of the most stirring sci-fi of the 1980s. Much to the chagrin of the galactic Patrons, humanity has 'uplifted' dolphins to sentiency. An exploration vessel crewed by humans and dolphins discovers the fate of the ancient Progenitors. They battle Patron-ised forces to get the secret home. Brilliant Brin.

Speaker for the Dead
by Orson Scott Card (1986)

Riveting sequel to Ender's Game. Ender Wiggin gets chance at redemption for his unintentional xenocide of an alien race. For thousands of planetary years he travels the galaxy performing community-healing ceremonies for the dead. The alien Hive Queen he is carrying finds a home, but the Galactic Federation is not pleased. Sci-fi at its best.

The Player Of Games
by Iain M Banks (1988)

Part of the on-going Culture sequence set in a far-future where humanity dominates the galaxy, living idyllic high-tech lifestyles free from scarcity or need. A master player of games gets invited to a tournament at the small alien Empire of Azad - replete with all the imperial trappings. An interesting clash of cultures ensues. Close to best in the series.

Xenocide [S3]
by Orson Scott Card (1991)

The third instalment of Card's Ender Saga has our philosophically embattled hero on the planet Lusitania trying to neutralise an extraordinarily adaptive virus as a Starways Congress fleet sent to quell the rebellious colony closes in. Hidden on the planet is the last remaining Hive Queen who may hold the key to humanity's future. Complex, so best to start with the first two instalments.