Is there a way to mirror and duplicate in one action? I have this cube:


When I mirror it around the x-axis I get this:


but I want this, so that the object is mirrored and duplicated:


Currently, I can do that by copy-pasting the cube then mirroring the duplicate cube (leaving the original cube in place), but it feels like there should be a better way.

How do I mirror an object such that it is duplicated, leaving the original in place?
Use a mirror modifier.

All you need to do is add the mirror modifier, and set its Axis to Y... 

Assuming you have the object origin at the scene center, and your cube positioned where you want it.