It depends on what you want. If you want full armed Dúnedain like the Grey Company then it should big horses and tall guys with chainmail, spears, swords, shields and cloaks.
I think these miatures are perfect for that (Gamezone, mounted squires from the Feudal Knights range):
On the other hand, if you want rangers in their regular scout gear then it would be leather armour, lighter horses, hooded cloaks, swords and maybe spears and bows (however I don't think they had mounted archers).
Something like this guy, which is a mounted ranger by Mithril Miniatures:
But if you want them to be compatible with the tiny GW LotR range, then you can't use any of the above. In that case, mayve Perry Miniatures' Crusade range has something interesting for you: