The list is still as long as my arm, in spite of the 50+ books I already have, but here're some highlights.
Champions of Valor
Champions of Ruin (can't have one without the other, eh?)
The rest of the MM's. I've only got the first two and FF.
Stronghold Builder's guidebook
Magic of Faerun. (I've got every other magic of X already
And more still. These are just off the top of my head.
Oh, I still need to replace my copy of Savage Species that was destroyed. Stupid moldy storage unit.