Are you trying to track the motions of stars -- or just pan the head electrically?
Some star tracking heads (which normally rotate at "sidereal" speed (the angular speed at which the Earth rotates on it's axis) but some of these can be set to higher speeds. E.g. a Losmandy StarLapse can be set to rotate at up to 240 degrees per hour. For a "tracking" head, it's the most versatile (the others usually only have a few speeds).
And of course there's the above-mentioned Gigapan heads.