Well met!
Some of my faves...
1. 3e FRCS. The model by which all 3e campaign books should have followed.
2. Forgotten Realms Adventures. One of my big intros into the Realms.
3. Grey/Gold boxed set. I started with the original grey box, but got the revised gold box. Great product.
4. Gods books (Faiths & Avatars, Powers & Pantheons, and Demihuman Deities for 2e, Faiths & Pantheons for 3e). Best info on the gods of Faerun out there. I just loved the info on specialty priests in the 2e books.
5. Heroes and Villains Lorebooks. I have the original one that told of the early novel characters that I fell in love with, then the revised versions later on in 2e. Great guide to characters.
6. 2e Harpers book. Tons of info.
7. Drow of the Underdark/Menzoberranzan. The original book (and even its 3e successor) and Menzoberranzan will be the foundation for the drow for me for time immemorial.
8. Al-Qadim book. I know, technically a different setting, it's still part of the FR world. Fantastic source for Arabian Adventures.
9. Magic of Faerun. One of my favorite 3e FR books. Has the gnome artificer prestige class. Great tinker gnome concept.
10. Under Illefarn. One of the best modules for a first-time DM. Complete with info on the town of Daggerford and its residents for DMs to create a home town for heroes. A few glitches in the last adventure, though.
11. Ruins of Myth Drannor. Just a fun boxed set.
12. Grand History of the Realms. Magnificent.
All I can think of for now.