Elves might be a good idea - the Dunedain worked often with the Sons of Elrond, so they could bring a contingent of Rivendell Elves. A cool (but pricey) idea might be to bring a Rivendell Knight Captain and a group of Rivendell Knights (from the Hobbit) to represent far ranging Hunting Parties from Rivendell.
Otherwise, under Halbarad they went to Rohan to search for Aragorn - you could have some Rohan (as has already been suggested). You could take it further and theme them during the Battle of Pelennor Fields, which would open up Gondor, The Fiefdoms, Rohan and elements of the Fellowship as options.
Plenty of opportunity to have some fun, I think.