Been romping with my Undead until...

[Saxon]

I just thought of something related. More generally, flying troops that can hit the rearward commanders will also work well, though most that I can think of are living.

I also like The Pelt of Feniris (I think that is the name). It does not fit in with your undead theme, but having wolves line both sides of the battle is a nice distraction. I have found that they do not do much damage, but they distract your opponent from the main force. Right now I have a lot of spell casters, so the extra couple of turns the enemy spends cleaning up the close by wolves are a couple of extra turns of spell casting. In your case, having the priests mess about with the wolves in close combat give the rest of your troops more time to advance.