[colanderman]

The 2D projection of a spherical shell isn't a uniform disc – it does indeed look more or less like a ring. (Consider the rough analogy of a swinging pendulum – it spends most of its time near the edges of its swing.)

[Thrymr]

An orbital is not a spherical shell.

Edit: These are probably higher energy states. e.g., the 6s orbital: http://en.wikipedia.org/wiki/File:HydrogenOrbitalsN6L0M0.png

edit 2: Previous comment was still not correct. More plots of electron density for different energy states: http://cronodon.com/Atomic/AtomTech4.html

[colanderman]

From the page you linked: "Notice that the electron is most likely to be found at one Bohr radius from the centre, in approximate agreement with the classical atomic model." That's approximately a spherical shell.

Why would these be such high-energy states?