I've run over a dead deer before, too. It was late at night and by the time it was noticed, it was too late to avoid without a dangerously drastic maneuver. No damage done, fortunately.
I once saw a potted tree in a lane. It had fallen off a landscape truck. The truck was pulled off to the side, backing up to retrieve the tree. At least they weren't leaving it there in the road.
Ladders in the roadway are pretty common, too. They fall off work truks when a bungee cord breaks or comes loose.
When I was driving to work up I-77 one freezing morning in Ohio, I looked in my rear-view and saw BLACK. Solid black in your rear-view mirtror is a bit unnerving, I must say. Upon closer inspection, I realize that my bedliner had come loose and was flapping up to the point it was obscuring my rear-view. Moments later, my bedliner was airborne.
Traffic was relatively light, fortunately, but I think it scared the **** out of a Dodge Neon about 8 car lengths behind me. The bedliner flew up about 30 feet or so and drifted off to the shoulder, where it came to rest, not blocing any traffic lanes.
I continued on my way to work and had a good laugh about it. IIRC, the power was out that day, so they sent us home.