Relativistic Space Travel Fiction

Now that there's at least a semiserious project to launch microsails to Alpha Centauri at a third of the speed of light, and the literature on beam-pushed spacecraft (going back at least to Bob Forward the 60's) might be gaining some traction, we can look ahead to what kind of interstellar civilization might result from ships able to go close to, though not faster, than light. While there are some literary examples from people like Haldeman, Forward, and Anderson, it's largely virgin territory for writers. If we dump the FTL and Generation ship tropes, what have we got?