I have created some scripts to assist with scene creation in Blender. These scripts are free to use and modify with attribution. I am distributing them under the MIT license http://opensource.org/licenses/mit-license.php.
This blender add-on moves the selected object(s) to the centre of the ground plane.
This blender add-on finds the lowest point on the selected object(s) and aligns that lowest point to the ground plane while maintaining relationships between selected objects.
This blender add-on resizes the selected object(s) to fit within the specified maximum height. Proportions are maintained for all selected objects. The Default maximum is 2 Blender units but this can be changed by clicking on the text.