I have heard of alot of the same, such as old mattress box springs, chain link fences, etc. I know someone else who simply dragged a 2x12 beam or similar behind them.
I just heard the most interesting one the other day. A farmer told me he used to cut down a couple of birch trees and secure them upside down to his loader bucket. He would then drive around backwards dragging the branches and leaves over the seeded areas. He said it worked very well.
You could always buy a drag harrow for $180 at your local TSC. They generally have pretty beefy tines and some can be reversed for digging in.