The Hubble Space Telescope has been used to assemble a time-lapse color movie showing a full 16-hour rotation of Neptune. An animation of one rotation is shown in the adjacent image; here is a more extensive MPEG movie (492 kB) made from a series of Hubble observations (Ref). These images show a powerful equatorial jet stream, immense storms, and dark spot in Neptune's northern hemisphere (more info).
The Voyager 2 flyby in 1989 revealed strong winds, bright, high-altitude clouds, and two large dark spots attributed to long-lived giant storm systems. Tracking of these features indicated wind speeds as large as 730 miles per hour. The largest dark storm systems, called the "Great Dark Spot", is shown in the image adjacent left. It resembles Jupiter's Great Red Spot (more info).
The interior is presumed to contain a rocky core with an icy mantle topped by a deep layer of liquid hydrogen. Voyager 2's instruments detected a complex magnetic field. Like Uranus, the field is tipped with respect to the axis of rotation and offset from the center (the tilt is 50 degrees for Neptune, compared with 60 degrees for Uranus). However, the field is somewhat weaker than for Uranus.
As for Uranus, it is speculated that this magnetic field my originate in a conducting shell not far below the clouds, rather than deep in the interior as for Jupiter or the Earth. In that case, the conducting material would not be metallic hydrogen, as for Jupiter, or iron and nickel, as for the Earth. As noted earlier for Uranus, a mixture of water, methane, and ammonia under the right pressure could be responsible.