I strongly second the recommendation for Diaspora. The story begins about 1000 years in the future, with characters that are trans-human, or post-human. Start

I strongly second the recommendation for Diaspora. The story begins about 1000 years in the future, with characters that are trans-human, or post-human. Starting from that baseline of normalcy, then it gets weird. But it's not weird for the sake of weirdness. The story is grounded in logic and built around rational exploration of deeply philosophical ideas. The book can be challenging at times, but only because the concepts it explores are so deep. The writing, IMHO, is very lucid. Egan wants to bring you into these ideas, not drive you away through inscrutable prose.