I used to farm the Tangleroot quest chain in my early days for collectibles and loot. It seemed to have a higher droprate of Medium Eberron Dragonshards, Fragrant Drowshood and Lightning-Split Soarwood. One run-through would usually yield 1-2 medium shards, 1-3 fragrant and if lucky 1 lightning. I did run around and grabbed all collectibles on every stage of the quests though.
Anyway, it took a little bit of time but it was how I built my fortune.