Prince Imrahil and the Knights of Dol Amroth.
Haradrim and the men of Far Harad.
Elrond, Glorfindel, Elendil, Isildur, with Third Age Men of Gondor.
Faramir mounted with the Minas Tirith cavalry.
10mm "ghost" army (the Oathbreakers).
Not a character, but the massive battering ram, Grond. That would be a fantastic addition to a siege game.
And lastly, a 10mm scale Minas Tirith. A paper model would be perfect for this. Don't need all seven levels as such, but maybe enough to have two or three levels. Probably too big a project.