Stranger in a Strange Land
by Robert A Heinlein (1961)

No respectable hippie-era pad was complete without a copy of Stranger lying on a beanbag somewhere. Human raised by Martians arrives back on Earth, inherits a fortune and is indoctrinated by a Heinlein-like author. He becomes a messiah and free-love abounds.  A controversial bestseller in its day and still manages to raise some eyebrows.

Lord of Light
by Roger Zelazny (1967)

Zelazny's finest novel focuses on a starship crew that takes over a colony world and becomes technologically-enhanced Hindu 'gods'. Mind-transfers and cloning keep it all humming along nicely until a retired god throws a karmic dose of Buddhism into the mix. Despite the deity war that ensues - just the tonic for the Summer of Love.

Behold the Man
by Michael Moorcock (1969)

The son of a Jewish-Austrian immigrant travels back in time to find out the truth about Christ - and the truth is that the one and only true Lord is not all he's cracked up to be. The hero goes on to play out his messianic tendencies. A provocative look at the nature of religion and the importance of tolerance towards others. Moorcock's best sci-fi novel.

The Fountains of Paradise
by Arthur C Clarke (1979)

Clarke's best work from his later years depicts the age-old conflict between man and God. Hotshot engineer wants to build a 36,000km high elevator to the outer-atmosphere. If technical, political and financial problems aren't enough - the only viable place to build it from happens to be a sacred mountain with a monastery on top.

VALIS
by Philip K Dick (1981)

Drugged-out and nearing the end, Philip K Dick's version of religious anti-salvation may be a little hard for believers to take. God, as it turns out, is a virus perpetrated upon us by an orbiting satellite. The 'hero' goes looking for some theological solutions, thus giving the author the chance to have his somewhat bizarre psychedelic say.

Neverness
by David Zindell (1988)

Like most good authors mathematician Zindell stuck with what he knew best for his stunning debut. The hero becomes a master pilot in the Order of Mystic Mathematicians and sets off into the cosmos where he runs into a computer goddess and learns a thing or two about immortality. In the city of Neverness he rebels against his father, the Lord Pilot. Heavy stuff at times.

Hyperion
by Dan Simmons (1989)

Canterbury Tales in space. Human ascendancy in the galaxy is under siege as seven pilgrims set off for the Time Tombs to find the creature called Shrike. Along the way they trade their stories - each one harbouring a dark secret. Well constructed high-tech future that adroitly mixes religion and revelation into the plot. At the top of the class.

The Sparrow
by Mary Doria Russell (1996)

While the UN procrastinates, the Society of Jesus swings into action and sends out a first contact expedition after exquisite ET songs are picked up by a listening post. Forty years later in 2059 the lone surviving Jesuit returns to explain how it all went wrong. Russell compellingly challenges our convictions and humanity for the better.