Shape:
* The frisbee soared like a flying saucer.
* It was as flat as a pancake, but with a much more exciting journey.
* The frisbee spun like a spinning top, but in the air.
Flight:
* The frisbee glided through the air like a bird.
* It danced through the sky like a leaf in the wind.
* The frisbee zipped through the air like a bullet.
Use:
* They tossed the frisbee back and forth like a game of catch with a giant, flat toy.
* The frisbee sailed across the field like a message in a bottle on the breeze.
* He threw the frisbee with the grace of a dancer, watching it curve through the air.
You can choose the simile that best suits your context and desired imagery.