Well, yesterday was my last game until I finish moving, which will probably be in about a week, week and a half due to unpacking.
Now here are the books that players have used for feats, spells, options, etc...
Unearthed Arcana: I talked one of the players into taking the Item Familiar to see how it works. At first he hated the idea but after much reading, loved it.
Love and War: One of the players, the mage with the greatsword, has a few spells from this book from the section on arcane knights (expect a review soon!)
Book of Exalted Deeds: One player, a paladin-fighter, has a few feats from this book.
Complete Warrior: Some feats from this book in play.
Tome of Horrors: I updated the Cambion with a feat and gave him some armor.
Dragon Magazine: The one recently celebrating the 'evil' of D&D with base classes and PrCs, not to mention the main villain, the Ebon Maw. Great fight right there.
Unapproachable East: The party has been hiding out in Rashemen for a while. They've allied with a few characters who have the PrCs from this book, as well as some of the more unique races from this setting. Last time they fought some blighted treants and their Blightlord master. They're originally here chasing some Nar who have bonded themselves to...
Deluxe Book of Templates: Still using the Ebon Servitor Template. The Nar barbarians have allied themselves with the Ebon Maw and he gives them this tempalte to represent their demonic heritage (Nar culture has demonbinders and other goodies in their past).
Artifacts of the Ancients: One of the player's, a mage, has the dragon slaying sword and has taken a PrC (Spell Scion) from this book.
Seafarer's Handbook: I've used a few of the boats here as the party went down the Lake and through the River in the Unapproachable East.
I'm sure that I'm missing a few. I mean there are the basics like the DMG, PHB and MM. and the Kalamar Screen (gotta love that Pizza Matrix.)