Dwarves Deep has to be one of the BEST Forgotten Realms accessories ever made together with Old Empires, Moonsea and Dreams of Red Wizards! It sheds light on the DWARVES of the Forgotten Realms, their exotic lands and their proud heritage. Their distinct culture, history, and civilization will win you over for sure!
Ranging from background history, to city and social descriptions, to important people and characters, to the respective gods and pantheons, to dwarven spells and magical items, to details of the dwarven language and kingdoms, to new monsters and half-dwarves (!!!), to adventure hooks and maps, this accessory has it all.
For other FR references/adventures, I recommend: the Old Empires accessory on Chessenta, Mulhorand, and Unther, the Dreams of Red Wizards accessory on Thay, the Pirates of the Fallen Stars, Moonsea, and Draconimicon accessories, as well as the Ruins of Myth Drannor Box Set Adventure, and the Ruins of Zhentil Keep Box Set Adventure (they are Second Edition AD&D, out of print and it will take a bit of searching, but it's well worth it).
For a more complete picture on Dwarves, I STRONGLY recommend the Complete book of Dwarves which provides additional information relating to the hardy stone-loving people, thus supplementing the existing material.
For an updated edition of events on Faerun's Dwarves see the Third Edition Forgotten Realms Campaign Setting, which even though is quite expensive, it is still very useful to all FR fans!
In conclusion, if you have a soft spot for the little stout short-tempered dwarvenfolk, try and get your hands on a copy of the Dwarves Deep accessory. You will not regret it! Trust me...