B777, DC10, B747SP etc all have double hinged rudders. They are there, as has been mentioned, to increase the contol surfaces effectiveness.
In the case of the DC10 it's because there is an engine stuffed half way up the fin, result is a very small control surface.
The B747SP has (I think) the same size fin as the standard B747 but as the moment arm is much shorter (fuselage chopped) then a more effective rudder was required.
B777 is all to do with engine out at T/O power. A hugely effective rudder is required when you lose 100,000 lbs of thrust on one side. I think it's deflected automatically too if I recall.
Don't know much about the 727 but I assume it is as described for similar reasons as the DC10.
Hope this helps.
