Here is a short list of observable proofs for a flat earth:
1. There is no visible curvature.
2. All bodies of water are absolutely level.
3. All aircraft move over a stationary flat plain.
Arguments against these facts contradict sensory perception.
--Dave
Alright...
I'll bite.
I am adding The Coriolis effect as evidence of a round earth. It is most apparent in the path of an object moving longitudinally. On the Earth an object that moves along a north-south path, or longitudinal line, will undergo apparent deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Snipers have to learn to correct for this when they pull off the super long shots.