In the days when we played Lord of the Rings, I loved my Easterling/Khandish alliance force. It was so unique among LOTR armies, nobody had any idea of what to make of it at the one tournament event where they appeared.
I enjoyed that advantage, and seeing people furiously waste precious ranged shots at the chariots instead of what they should have focused on.
To expand on that idea, my next plan was tom combine mounted Morghul Knights with a Spider Queen, some regular spiders and the little swarms.
The Spiders were insanely fast, and could go through any kind of terrain like open ground. This could flush out prey from rough terrain into the open for the Morgul Knights to run down. Also, the Spider Queen would help to turn the odds in a scrum to my favor by creating some broods on the spot and sending them forward into existing combats.
I still have the Knights and the Spider Queen, along with the swarms. The original spiders were regular Goblin Spider riders from Warhammer. I'm sure that I could find some interesting spider miniatures today!
I had to convert these spiders a bit, to resculpt the areas where the goblin rider would have been.
Here's an image of the conversion process, with a link to the original post:
He's also here: