Based on Neil Blevins' object planter. This script allows you to select two sets of objects and plant / parent them to another set of geometry that is "below" it. Ideal use: you have a bunch of props and need to plant/parent them onto multiple ground pieces... you can select all the trees, select all the ground pieces, and it'll automatically parent to the object below it.
*Sometimes it will parent to wrong objects... i find that a reset xform on the parent objects help.
*Zoffset takes the ray and places it higher to originate from (in case your object is actually lower than your ground piece, or is really close.
*BBox check -- for irregular shapes, (sometimes the center of the object isn't above a ground piece, but the mesh is) will subdivide each object into 4 rays to try and ensure that it hits an object ... will possibly further this later