Luminous

Another of Egan's phenomenal collection of short philosophy fiction in the guise of science fiction. Several explorations of the nature of consciousness from viewpoints such as machine/brain uploads and interfaces and brain chemistry; the nature of space-time and personal identity mixed together as copies of people fall into a black hole or not and many more.
I think his short story collections are better than the full-length novels as they start you thinking without the slight unravelling when the premise is pushed past its limits.