What is a good hard sci-fi/space opera book to read?

I would recommend Iain Banks' "Culture" novels. A few titles includes "The Player of Games", "Use of Weapons", "Consider Phlebas", "Inversions", "Look to Windward".

I would also recommend Larry Niven's Ringworld series.

Check out the Deathstalker series by Simon R. Green. Awesome book series. It can get pretty complex. And before you ask. No. I does not have anything to do with that crappy movie series from the 80's.

The series is set in a far-future, fictional universe, dominated by a vast and powerful human empire that has fallen from its ancient beginnings into cruelty, decadence and oppression. Alien species when encountered are subjugated or exterminated; internal dissent is ruthlessly put down, and power is concentrated in the hands of a psychotic empress (known as the "Iron Bitch") and a number of aristocratic families, or clans.

Under the justification of protecting the empire from external threats, the empress maintains the status quo by playing off different groups against one another, preventing any organisation from becoming powerful enough to challenge her rule. Cloning is commonplace, with clones being regarded as non-people for use as expendable slave labour. Some people, known generically as espers, have various psychic powers including telekinesis, telepathy and teleportation – these, too, are carefully regulated and exploited by the empire.

The vast majority of imperial citizens, while denied many forms of political self-expression, appear to lead fairly normal lives under the fiefdoms of the different clans. The author draws a parallel to certain periods of the Roman Empire, with the citizenry being kept compliant through the use of public holidays and spectacles such as gladiatorial games. Although a parliament exists, its autonomy and influence are trivial – in large part due to the widespread corruption that permeates every facet of the empire's institutions. The empire's official religion, the Church of Christ the Warrior, acts as an arm of the imperial throne and maintains its own military forces to counterbalance those of the clans.