I just started The First and Last Men by Olaf Stapledon, but I JUST started it so I don't have anything to share yet.
I just finished Encounter with Tiber by Buzz Aldrin. Really good and realistic fiction, I especially like the way he makes the aliens seem both alien and familiar. Their prejudices that they bring to the stars resonated in a way that I find hard to describe.
In recent past I finished Dan Simmons' Hyperion 4-novel set. (Hyperion, Fall of Hyperion, Endymion, Rise of Endymion). Really fantastic hard sci-fi that also has engrossing characters. Highly recommended.