The World Born Dead
Clerics and Druid spells
Clerics and Druids now get access to all divine spells on their respective spell lists that are found in Divine Power and the Players Handbook. Every four levels they are allowed to add either a Cleric or Druid spell of the highest spell level they can cast from another supplement to their respective spell lists. To be clear: Druids can only pick druid spells, and clerics can only pick cleric spells.
Supplementary spells beyond that can be researched using the method in the Dungeons Master Guide, i.e. it takes one day per spell and that such research costs twice what it would normally cost to have an NPC cast that spell for the character.