Is a sphere (possibly flattened) the only possible shape for a planet?

I think it is very hard for a planet to be of some other shape, rather than a sphere, 'coz gravitational pool will attract that mass whatever its former shape may be from the centre.

Sorry couldn't be of much help though.

Not without two forces tugging at the torus in opposing directions: one from the centre of the torus and one from outside the torus. Otherwise, the torus will just collapse into a sphere due to gravity, or rip apart because there is not enough gravity to hold it together.

An example of a torus-like shape in our solar system are the rings of Saturn. However, they are kept in place by the planet's gravity from the inside and the system of satellites from the outside.

If you believe in the multiverse hypothesis, yes there could be a universe that may have completely different physics than ours.

Then it's possible. But I don't think it's possible in the universe we live in.

I have to admit though, a torus shaped planet would be cool.

Planets are spheres by definition. For an object to be considered a planet, it must be large enough for it's own gravity to have pulled it into a sphere. If it's not a sphere, it's not a planet but something else.

http://en.wikipedia.org/wiki/Planet

The current definition of a "planet" includes that it be spheroid; this disqualifies irregularly shaped objects like asteroids.