A create undead spell for necromancers (wizards) or clerics would be a nice touch, I think. While it's fun to 'control undead' as a wizard or animate dead, I think having either the ability to use animate dead on other undeads; or have a new 'create undead' spell for ghouls, mummies, etc. would be nice. This gives that evil, undead army appeal. Allowing us, as the caster, to dabble in 'research' of necromancy to come up with 'new types of undead'.
My proposition for 'create undead' would simply be having the undead created fit into a player's pet slot. Not like the animate dead spell, but like purchasing a mount, follower, or slave.
A spell is more preferable for the roleplay aspect but a vendor for undead could be another idea.