This one looks more impressive in real life than you'd think from the description -- though maybe it takes an interest in the uses of yogurt containers to really appreciate.
I mounted a clear acrylic ball in a clear yogurt lid, by cutting an X in the lid and pushing the ball in the slot. Then I pinned the side of the lid to the wall so it stuck out horizontally.
It really does look like warped space-time. I swear. And it throws a nice reflection and shadow, too.