I always had problem with create zombie/skeleton spells. Make it cost power and your necromancer runs around with a power of 3. Make it so it dont cost power and your necro runs around with a horde larger the one Xerxes invade Greece with .
One thing I been toying with is to allow certain evil types to use power of people they sacrifice for certain enchantments. Perhaps if the sacrifice is worthy they get 1% of the victims power to store in a pool for enchantments or make zombies/skeletons