Just WotC books? WotC and third party? Either way, you're likely to get some pretty long answers -- are you curious for a specific reason, or just curious?
For full D&D (including licensed D&D products) and not just d20:
DMG 3.0
MM 3.0
Forgotten Realms Campaign Setting
Magic of Faerun
Dragonlance Campaign Setting
Dragonlance Age of Mortals
Ravenloft Campaign Setting
Ravenloft Lords of Darkness
Ravenloft Denizens of Darkness (the 3.0 one)
Ravenloft Heroes of Light
Ravenloft Champions of Darkness
Book of Challenges
Sword and Fist
Tome and Blood
Return to the Temple of Elemental Evil
Monster Manual II
Ravenloft Van Richten's Guide to the Living Dead
Ravenloft Gazetteer V
Kalamar Harvest of Darkness
Kalamar (another module, forgot the name)
Complete Warrior
Unearthed Arcana
Lord of the Iron Fortress
Psionics Handbook (3.0)
I don't own a 3e PH anymore, just the srd. But still that's 24 3e D&D books. It is a small fraction of my whole D&D (prior editions) or d20 collections.
It would be easier to list what I don't have. I don't have a life, saving account or decent car......
Seriously-
I have about 100 books ranging from Core, FR Realms, Eberron, Scarred Lands, Ravenloft, Oathbound, Kalamar and then a bit of this and that of other companies and products from Malhavoc, Necromancer and others.
I didn't include all D20 system books. Those are just WotC D&D books. I'm probably forgetting a couple as well, since I did this from memory.
(Pardon any unusual abbreviations.)
Bound to be some really long lists here! I don't have anywhere close to all of them, but I do have more than I am likely to hunt down! The bulk of my collection are the core books and a fair amount of Forgotten Realms sourcebooks.