This is where I first came into contact with Australian author Greg Egan, an Interzone regular and prime purveyor of this latter type of story. Egan's 1997 novel Diaspora is a superb example of his work. It starts toward the end of the 30th century when humanity has split into different strains – as software entities living rapid yet immortal lives in virtual reality, or interacting with the physical world inhabiting robotic bodies, or a few 'fleshers', humans who doggedly remain attached to their biological reality. An unforeseen astrophysical disaster causes some of the digital personalities to send out copies of themselves to explore the universe in search of somewhere safe from potential annihilation from cosmic accidents.
This is not just an updating of Stapledon's Last and First Men or Wells' The Time Machine to the information age, where biological evolution continues seamlessly into electronic, but an exploration of what it means to be human, to be conscious, to be intelligent. Is the only way to be human to remain in direct contact with the physical world and live a life measured in decades, or can a piece of software that is at least as complex and possessed of its own drives and personality and autonomy, that wants to survive and learn and has morals and ethics be also considered human? As the environments in which humans live are artificial anyway, is living in an entirely virtual world any less valid?
Along with a story that presents these issues, Egan takes us into areas of multi-dimensional maths and wormhole physics that stretch the readers' minds just as much, all told with a clarity and skill that makes Egan one of the finest and most important writers working in SF today.
Read this if you like Neal Stephenson and Charles Stross. Other books on a similar theme include Stross' Saturn's Children and the wonderful Natural History by Justina Robson (both of whom are from Leeds, which is an interesting coincidence).