Two blue marbles.
Two water, life baring worlds in a Mars/Earth type orbit would inspire intelligent life to eventually travel and visit each other. Much sooner than it took us to visit our Moon, I'm sure. Would there be peace(trading, etc) or war. What if only one would have given way to intelligent life? What if giant dinos were at the top of the food chain on one, but not the other? Would they have moons of their own? Mars has two.... sort of.
Speaking of looking up. Seeing the moon (long after sunrise too) in the early mornings this week has been a treat.