lol'd at this last experiment on the link Talon posted.
3) Get High! <-FAIL!!
Ok, this one you really can't do at home, but you can do it out in the world. Stand on the ground and look around you. What's the farthest you can see? Maybe it's a building, tree, or mountain. Now, find some place very close to it where you can get a much higher vantage point. (This also works if you're on a jet and about to take off.) Notice how in the higher place you can see much farther? You can see more of the world the higher you get. This shows the world is flat because the higher you go, the easier it is to see over obstacles. At the same time, it shows the world cannot be spherical. Because if the world was curved, the far distance would forever remain out of view because of the Earth's curvature. It would eternally be over the horizon.
If the Earth was a sphere, it would not matter how high you went, you would still see the same thing. Since this is not the case, the Earth is flat.