I just finished reading Vacuum Diagrams by Stephen Baxter - it's a fanstastic epic spanning 5 million years into the future. It rates right up there with Diaspora by Greg Egan, with plenty of "hard" science and imaginative situations. I feel I have to somehow amend my original list of five to include this one.
Thanks again, Tielhard, for introducing me to this great author, and thanks also to Xaosdog for turning me on to Greg Egan and Linda Nagata. I've read everything I can get my hands on by all of them, and they never fail to please!
"Patterns are set in one place and time, to be followed to the end of all years to come". (Andre Norton)