Necromancer cleric rock
Better survivors than non-undead arcane necromancers anyway...
PrC: Master of Shrouds from Liber Mortis. You lose a level of spell-casting but you still get nine levels of spell-casting, extra abilities and your rebuke undead stays up. Especially appropriate if you're using the
summon undead spells from LM as one of the pre-reqs for the class is Augment Summoning and one of special abilities grants a bonus on attack and undead to any summoned undead.
Avoid True Necromancer unless you want to add arcane spell casting and all that entails to the mix. Master of Shrouds is much better for straight cleric.
Feats: Aside from the corpse-crafter feats in LM, I'd suggest Extra Turning and Improved Turning from the PHB, Heighten Turning, Empowered Turning and Quicken Turning from LM. That last feat allows you to bolster your undead as a free action
Consider Tomb-Tainted Soul so that you don't have to worry about memorising any pesky
cure spells to keep yourself alive and Undead Leadership for even more undead minions.
Domains: The real trick. The Death domain isn't actually that good for a undead specialist as the granted ability doesn't help with hordes of undead. It is a fairly good offensive ability but I'd rather have Deathbound (control three times your CL in undead) and Undeath (Extra Turning feat).
Hope that helps. Here's a non-mechanical thought: Buy your necro-cleric a skull mask, a big black cloak and a scythe. Cast
air walk. Have a floating cloaked figure with a skull for a face and a scythe