I would like to see a vignette of the Watcher in the Water at the West Gate of Moria. Mithril has produced Dragons, Spiders, the Balrog, and every manner of Creature fair or foul except the Watcher. It would have a base as the pool of water and a strip of shore before the Gates. Several tentacles would break the surface, one which has ensnared Frodo by the ankle on the shore. Sam would be kneeling, hacking at the tentacle with a knife in an effort to free his master.
If not too expensive to produce, The opened West Gates of Moria could form one side of the vignette, with the requisite designs and "Say 'Friend' and enter" in Elvish upon surface of the gates. Gandalf could be standing on the threshold, about to enter, looking back at the scene at the water's edge.
If too costly to include, the West Gates of Moria could be a companion piece produced in the future.
"I felt that something horrible was near from the moment that my foot first touched the water," said Frodo. "What was the thing, or were there many of them?"
"I do not Know," answered Gandalf; "but the arms all were guided by one purpose. Something has crept, or has been driven out of dark waters under the mountains. There are older and fouler things than Orcs in the deep places of the world."
There have been a lot of great suggestions, but this momentous scene deserves to be produced--The Watcher in the Water is too important a creature to leave out!
OK, my official suggestion: I know we just had the death of Boromir but I would love to see Boromir, dead, in an elven boat, with his broken horn on his lap, the weapons of his enemies piled around him, floating down the river. Barring that, a figure of Theodred in some pose.