It seems that you've settled on rangers then, lol
Out of any ranger unit, Grey Company are the definites (unless you already had them int he army, obviously, lol
). Grey Company are just better in all respects.
Gildor's Household aren;t really allies since they're in the same list, but they are one of the best units in the game, IMO. Ambush, elven cloaks, longbows , the added defence bonus from appearing in terrain, plus Gildor has 2 spells per turn (best used to increase shooting and to cast Nature's Wrath as a default plan, unless better opportunities arise).
As for just any allies, Dwarfs will be VERY tough compared to your normal units and slightly cheaper, otherwise, go for the cheap as heck warriors of Minas Tirith. About half the points and the same or better defence. Twice as many bodies to soak up the flak.