Round shapes out of rectangular parts? Seems a little crazy but you can make one of these bad boys for yourself with normal 1x2s and basic building skills. Impress others or use as a wall decoration.
This circle is made out of standard rectangular Lego bricks. When enough bricks are stacked together they start to bend a bit and eventually you can complete a full circle.
Though smaller circles can be made, making one with 100 bricks per layer doesn't put too much stress on the bricks. I always use 3 layers of bricks because they hold better and have a lesser chance of exploding all over the room.