Let's see...
Undead Clerics could easily be Ltnts helping push the hordes...
Anything that spawns and can control it's minions can easily be controlled by one cleric. Take a Wight, control it, feed it bunches of people, and now you have an economy wight package.
If you want some fun magical typed skeletons, just use the spellstiched template. This can provide lots of extra little magical bonuses for the little guys to even the playing fields against characters. I did this once, and gave the little 'uns lesser orbs or MM's. The players were amazed at the ones and two's they originally encountered. Then in a massive battle 100 skeletons let go with 100 magic missles, and plowed over the first few ranks of the living. One player got zapped with 34 herself, and only skated by because of a brooch of shielding (everyone used to laugh at her for using it). Spellstiched, Great Fun!