For the TOS Movies I would say it was (in order from most underused):
Uhura, Sulu, Chekov, Scotty
And then for the TNG Movies (in the same order):
Crusher, La Forge, Troi
Of course if you're including guest appearances just for the films there are a few others that could be added to the list: Ilia, Decker, Hawk (are the main ones I always think about).
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)