I never use the Orc and Goblin shamans produced by GW for our game. The reason is because I somewhat respect the canon of Middle Earth: Magic is rare. And Orcs generally can't use magic. Obvious geek-knowledge.
But when it comes to creatures and monsters, I have a rather more relaxed and un-geeky approach, which is mainly because of a few sentences in Silmarillion where Morgoth's (?) monsters were described a little too unspecific. This allows for all kinds of creatures for the followers of general bad behavior to be created and used in the game.
I am surprised with GW that they haven't gone totally over the top with monstrous creatures in our games of Lord of the Rings. The only problem with this unusal show of restraint – from a company infamous for its giant skulls and giant weapons and spikes and bones poking out of everywhere – is that there are too few monsters and centerpieces for the goodguys in LotR. There are the Ents and Great Eagles. Sort of Glorfindel, at least if you play WotR. So, how to beef your armylist out? We have:
 Ents and Great Eagles (let's ignore the named variants for now).
 War Machines. We already have the Avenger Bolt thrower and Battlecry Trebuchet for Gondor. And a Siege Bow for dwarwes.
 Beorn. Guessing it will be released as a large monster (64mm or more) within a couple of years.
 Beornings. On 40mm bases? Feel free to do these yourself and use Cave Troll rules or whatever fits. In WotR they are intended as infantry, but nothing stops you from doing your own thing. Personally, I think bears are boring.
 Huorns. Remember that Huorns were fighting almost alongside with Rohan in one of the books. Thats canon right there!
 The Legions of Middle-Earth (LoME) speaks of Elf Chariots and Elf Catapults! These two entries opens up a whole new world of interesting (and highly decorated) projects. I will try to make one or the other before the end of 2013!
Above are more or less the official monsters or centerpieces for the good guys. A meager list. The following are my Golden Ideas. They are intended for people who can use their own minds and actually enjoy doing so. This is why each entry is explained in a slight way and is not minutely detailed.
 The Stone Guardian. Based on the púkelstones, or Pùkelman. Mentioned in the Books. I did my version very un-canonical because I wanted a more high fantasy look for the Edheldu army, since it was a more relaxed project. One could easily do it more understated, more "realistic" and overgrown with vines and branches and roots.
 Some sort of un-canonical Tree Spirit (also for Edheldu), I guess you could excuse it with some texts regarding Huorns or some First Age Elvish mumbo-jumbo, I haven't really bothered with that since it looked nice enough when it was done and suited well with the theme of mentioned army.
 Chariots or wagons can be done, IMO. They aren't that offending, even if there are no mentions of Gondor or Rohan using these. Why would they though, their horses are strong enough to carry a fully armoured rider.
The Dwarwes on the other hand are mentioned using wagons in Bilbo, but I guess those were civilian…
 Perhaps even a large carroccio (big wagon) rip-off for Gondor? Something with large flip-off banners and Citadel Guards with trumpets and more banners and more guards and armoured oxen or armoured horses pulling the whole thing!
 The centerpiece Trebuchet. With a nice base and some barrels and a banner blowing in the wind. And of course: A captain on a rock.
 Spawns. This one is the most controversial. At least for a gamer. For a person more concentrated on the pure hobby-part I guess you could do it. With "Spawns" I mean something good-natured that has been spawned by some Elf mage or whatever. Like the White Water horses in the books, and the movie. It would look a bit stupid, but not that much more stupid like the Kraken – a model which I, at least, like.
The "Spawns" will excuse a lot of creatures for the Elves, even if it is not in accordance to their description in the books, as pure and simple, everliving people etc etc, but whatever.
 Headquarters diorama. On a 64mm base, for Gondor. Just a collection of regular WoMT:s, with lower ranks, with maps and some special weapons or a signaling lantern. This idea I find interesting. It would in a way remind of the King's Champion.
The ideas above are more or less uncomplicated to crowbar into your hobby, except for possibly the spawns and Tree Spirits, but with some good will it's possible. So, how about Rohan and Erebor?
Rohan should stay what it is with its infantry and cavalry.
Erebor, though… hmm… perhaps a warmachine on wheels, with the risk of making it high fantasy, though. And besides, the dwarwes already have their Siege Bow. How did the dwarwes look at magic? Can one make some sort of Tolkinesque golem-like statue-whatever? Not that I would want to game with such an abomination. But we keep our minds open here and still stay within canon (sort of).
Is there any chance that the coastal parts of Gondor could have brought something back to fight for the main city? Some sort of beast from the South, or why not something from the North? One should look into Pelargir and the Fiefs and especially the sea-faring parts of Gondor for inspiration.
There you have it. I have decided to make the equivalence of a carroccio for Gondor. Already got the two ox-teams from Perry Miniatures, some piping to make wheels and a blister of old Guards of the Fountain Court and a few Citadel Guards and maybe even a regular Warrior of Minas Tirith or two to modify. The cross will be changed to something suitable, perhaps an "everburning" cauldron of fire from the top of the Citadel in MT and use dried tomatoes as flags (yes, burnished and washed with vinegar) with huge white trees sloppily painted on them. All based on a grand dragon base. Just need a better name and some rules. Just like this blog...