Gandalf would go as Saruman or he would just go uncloaked
(I really need to calm down with that!)
Sauron would go as Morgoth, his master and hero.
Aragorn would go as Haldir because he knows Arwen was cheating on him with him.
Arwen would go as Eowyn
Haldir would go as Aragorn because he wanted to get away from Arwen for a bit and that would become a problem because......
Eowyn would go as Arwen and go after Halidr because she thought it was actually Aragorn.
Théoden would go as himself tyring to get Arwen, who was actually his niece.
Pippin and Merry would go as each other because they don't want to act like anyone else.
Sam would go as Frodo because Frodo's is his hero and master.
Frodo would go as Sam because he can't get a girl and all the girls are after Sam. (that's not true but for now, let's think it is)
Legolas and Gimli would go as each other.
Faramir would go as Boromir.
Boromir would go as a Wight.
Denethor would go as the Human Torch.
Eomer would go as....... a tree!!! Just because he has no originality.