I voted Complete books (classic), Spell Compendium, Expanded Psionics and Monster Manuals. I also have much love for PHB2.
That's how it's been in my campaigns, but honestly, the headache grows with each additional book.
I'd love to run Core three books, Spell Comp, Magic Item Comp, and MAYBE Exp Psionics. Tack on a few feats from the Complete (classic) line and PHB2, but none of the classes. So simple!!
Maybe some Unearthed Arcana love, if only to get rid of some of the things I find silly or to add things that give the world a little bit more flavor (metamagic components, how I love thee).