*shrug* it's a matter of taste, really - one of the defining characteristics of the traditional undead is that they were one living beings - if you look at the epic spell rules, you can make a spell to turn virtually any corpse into virtually any undead critter - for the most part, simply pick an intelligent creature (if you are the GM) that's similar in form (similar size and basic body types - e.g., a large skeletal devourer might become a troll) (for corporeal undead - incorporeal undead pick any intelligent critter, as the body wasn't what was important).