I think that everybody knows about that in every map in the game has creeps, but they're only goblins, trolls, wolf/wargs, and thanks to the edain team, orcs.
But how like if we ad some other creep for give some variety, and I have ideas for every creep pack.
Humans=Bandit tent: There could be camps of humans that attack everybody they spot. Come on, either if the men had to fight against Morder, surely there are men that only fights for themselves, like thieves, raiders or assassins. The units could be the soldiers, the archers and the pikemen.
Elves=Old Tree: As we saw in some of the LoTR/Hobbit movies, the elves don't trust to who enters into their territories, either attacking them. This can be rogue elves that attacks whoever attacks their post, either if they're other elves. They only use basic archers.
Dwarven=Abandoned Mine: The dwarven, as we know, turn completely crazy when somebody tries to steal what is theirs (Gold, Jewels, Ore, whatever), and I think that some of them will mine around believing that there is gold or jewels where they're mining. Maybe this creeps attacks for protect what they found, without care if they're good or evil, dwarven included. They can be any of the basic melee units.
You could like to see this type of units mess around the map giving you and your rivals/allies problems during the game?