As Spells will be added soon, why not add Spellbooks?
Certain combinations can be made if elemental spellbooks are combined. This works similiar to Dragons.
Example: a Fire spellbook and a Water spellbook would make a Steam spellbook. Same goes with air and Earth- it'd make a Dust spellbook. The 4 main books (Water, Fire, Earth, Air) can be found in dungeons (not towers) and will also drop from naturally-generated Bookcases.
There's several tiers of spellbooks. This will work similiar to Skyrim (Short-range constant spells, long-range "bolt" spells etc.) and can all be affected by certain elements.