1) Use a telescope and you'll see all visible planets are round. Or just look at the moon. Thousands of people throughout the earth see views like this daily with their telescopes.
2) The earth's shadow during a lunar eclipse is round.
3) When a ship sails off to sea it disappears from the bottom up.
4) Patterns of stars change as you move north or south.
5) Time lapses of planets are often recorded and can be seen with a common telescope, showing multiple sides of different planets (aside from the moon, which is linked to the earth's gravitational pull).
6) Flight times don't make sense on a flat earth.
7) If planets were flat like pancakes, we'd likely see them looking like this, at least on occasion:
