Finding the true name of a demon.. I REALLY love this idea! Perhaps in order to summon demons/monsters etc you must know their true name? This would make the types and kinds of things you could summon "collectible" in nature, the same way as other loot in the world will hopefully be.
Also.. procedurally generated items, perhaps (along with unique "fixed" items?) Adds a LOT of replay value to almost any game. The industry seems to be focusing more heavily on this, and I love it. Something to think about.