For Book III of the Drow War you should have a copy of the Epic Level Handbook.
We never needed anything else. However the following books were brought to the gaming table by my players, which they used for thier character but were not necessary at all:
The Drow War
Complete Arcane by WOTC
Expanded Psionic Handbook by WOTC
Quintessential Paladin by Mongoose
Quintessential Paladin II by Mongoose
Mercenaries by AEG
Pocket Player's Guide by Mongoose
Forbidden Arcana by Ronin Arts
Ruins of the Dragonlord
Quintessential Chaosmage by Mongoose
Dragon Magic by Mongoose
Dragons by AEG
Complete Divine by WOTC
Quintessential Bard by Mongoose
Quintessential Bard II by Mongoose
Priests and Paladins of Fire by Ronin Arts
As the GM I am using:
PHB
DMG
MM
ELH (for Drow War III)
ExPsi (because my players enjoy psionics, but there is no need in the module for this)
and
A slew of the "A Dozen..." series by Ronin Arts to change up some of the treasture found (personal choice)
Bold are mandatory.
