I go canoeing in Manitoba every year, and hire a Beaver to fly me out. We tie the canoe on the outside float strut. This past year the pilot told me his boss tied a 206 jet ranger that went down on the outside of an Otter. And I remember seeing the Shuttle fly over piggybacked on a 747, what a sight!
You don't have to have actually flown the cargo to share, but if you've seen an unusual cargo load tied to a plane, let's hear it!