Spread Objects does what it says : it spreads the selected objects on an evenly spaced grid. It takes care of calculating the number of columns/rows and the spacing needed between each object and another.
Download "Spread.py", then go to Blender's file menu > user preferences > addons > install Select the file you have downloaded, install and enable it
From the Object menu select "Spread Objects" or "Spread Objects (keyframed)". The first only spreads the objects, and the latter adds initial position and final position keyframes for animation