Among Blish's works are four of particular noteworthyness.
All The Stars A Stage, the story of colony ships leaving a doomed world and attempting to reestablish their people and culture elsewhere. Although the ending has become a bit of a cliche, it still has strength, and fits very well into his sf/theological canon.
- Black Sunday and The Day After Judgement, or, what happens when a wealthy man tries to literally raise Hell on Earth. The monks gathered to combat the onset of Hell are named after golden age SF writers.
- The Seedling Stars, tales of the colonization of the galaxy by humanity. Includes the SF Hall of Fame story Surface Tension, the tale of tiny engineered humans struggling to survive in their watery microcosmos. They build a "starship" to travel to the next "planet" (but it's just another puddle on a desolate world).
The Cities in Flight
books are awesome, and have their own node.