1997, Orion, London
A hard-science fiction novel set post-flesh-humanity where sentient beings are part of a computer complex. When two colliding neutron stars threaten to destroy Earth, they begin a journey of discovery.
And then some!
This was an amazing book. It covered topics as varied as virtual reality, xenobiology, astrophysics, mathematics, evolutionary theory, chemistry, and a lot more which went well over my head. The setting of the story is so different to our world - usually it's hard for an author to separate a created universe from our own, but this attempt has been highly successful.
The ending was the most beautiful ending I have read in a long time.