You can set them up as rigid bodies and actually drop them to the ground. It’s sometimes faster than it might seem. For the ‘ground’ you should select passive as rigid body type, don’t forget to set Mesh as collision shape and it might be helpful to set the friction to 1, and set the sensitivity margin appropriately for the scale of your scene. After simulation, you can apply visual transforms(ctrl+a) and delete rigid body settings from the objects.
You can also use snapping if you don’t need your objects rotated. If Face is selected as snap element, the Snap Individual Elements on the Surface of Other Objects icon appears while in object mode as well, so you can view the scene from above and snap all the selected objects to the ground. It only snaps origin points of the selected objects, so it would be helpful if the origins were at the bottom of each object. It’s not for every situation, but is useful sometimes.
the grease scatter add-on is good for rubble and other things. you can also use a particle system set to emit objects of random size and rotation if desired. another option would be to run drop2ground in 2.55 and export the result.