Really darn good idea. Since each creed is hard, to make it would be excellent for collaboration to create a nice resource here. Perhaps as full subs linked to this one, so they can be voted on appropriately. Go to Comment
The secret for immortality has been discovered by an eccentric wizard/mad scientist. Its found you need to reapply once a month. As people stop dying, and the birth rate increases exponentially, people are forced into homelessness, because of the need for food reamins the same, and food is not being produced fast enough to feed the undying population. The PCs have to find the creator and kill him, and destroy production, to save the world from undying, unending torture from hungryness.