Some ideas came to me the other day regarding the origins of undead vs. the type of undead they are. Skeletons and Zombies come from the create undead type spells typically, right? What about the rest? We know that some undead create others of the same kind, but where did the first come from? Certainly there wasn't one progenitor of all of those types, especially when they are mindless beasts.
How about this: most undead come from the create undead type spells. Whether they are Skeleton or Zombie is a matter of deterioration. But whether they are another type has to do with how evil they were in their lives. Ghouls and Ghasts could be more evil versions of what was a Zombie, for example.
Next though we have the question of how to define evil. How about the 7 deadly sins? The more they committed in life, the more evil they were. This might also lead in some cases to types of undead being determined---like Ghouls and Ghasts always feeding = greed or gluttony or some combo of the two. Mummies sin was vanity and pride, hence the wrapping the body and mummification proceess. They might also have been greedy, as indicated by being buried with all their stuff.
Ghosts: Pushed to all manner of evil acts through greed for all that life had to offer, their reward is to constantly drain the life-span from their victims representing the waste of many years spent in life seeking that which couldn’t last.
Vampires: Have the body parts and the desire for sex, the sin of lust was their weakness, but their mere touch kills the victim they lust after.
Lich: The ultimate in undead, in that a form as been created which will allow it to fulfill the primary motivating force of its previous existence: Greed. Greed for power, obtained through wealth and magic, exercised through control of everything in existence. A lich knows that gluttony and lust are for lesser beings, not in control of base appetites. Wrath and envy are for those without the power to take what they want. Sloth is good to have in obedient servants without a will of their own, and pride is unnecessary to one with true power, as the manifestation of true power is reward enough. This leaves pure Greed as the sole reason to exist, greed for power, with the will focused through the eternity of lichdom to carry out the acquisition of power.
The Wraith/Wight/Spectre trilogy might represent something for the sins of wrath and/or envy: For those who have killed due to desire for something, or someone. They took a life, and are thus cursed to forever drain life and with each kill they are hungrier and hungrier, never to be satiated, making them more full of wrath. Their form is even more shadowy the more lives they took, representing the fact that even if they were to obtain that which they killed for, they would not be able to hold it.
Shadows might be sloth as the sin: Searching for the strength of will to achieve something in undeath, since they never had the strength of will to achieve it in life, all they manage to do is drain physical strength from their victims, as they fade to insubstantiality, never able to truly affect anything in the world again.
If most of them are created through the create undead type spells, then the cleric never knows what he is going to get every time he casts it. He better be powerful enough to control what he creates, or else it would be as likely to turn on its creator as the person the creator targeted them against.
How about those clerics and paladins who fight the undead? What if they happened to have been extremely virtuous in some of the qualities that are the direct opposite of the vices which they undead are attuned to? Chastity, temperence, patience, kindness, humility, diligence, and charity. The DM could allocate some bonus to turning or damage based on how the character has been roleplayed. Also, items owned by people who were particularly well known for these virtues would be more effective against the undead, and vice versa for being able to control them.
Anyhow, just some ideas. I have no charts or tables to offer, nor a unified system that ties it all together. I'm not good at that sort of thing. Just some ideas thrown out there---do what you want with them if you think they may be helpful.