Since the start of 3E, which (non-core) book have you used the most?

[Bodah]

FRCS, Magic of Faerun, Faiths and Pantheons, and the epic level handbook.

 

[Tidus4444]

sword and fist, tome and blood, and all Forgotten Realms

 

[Schmoe]

Book of Vile Darkness, with Masters of the Wild close behind. Most of my books have seen some use, but the problem is that I have too many supplements and not enough game!

 

[Cloakmaster]

FRCS.

 

[bret]

Tome & Blood

 

[Nifft]

Fiend Folio, Manual of the Planes and Book of Vile Darkness.

-- Nifft, DM of the Demon-Haunted Earth

 

[The_Gneech]

Creature Collection

Monsters of Faerun

Tome and Blood

Dungeon magazine (does that count?)

I used to use the Creature Catalog website quite a bit; now I have Tome of Horrors instead...

-The Gneech

 

[Nephet]

FRCS, Magic of Faerun, Lords of Darkness

 

[Ranes]

Right now, my answer to the original question would be RttToEE for the same reason Numion mentioned. However, ask me again a year from now and I strongly suspect the answer will be Savage Species.

 

[yangnome]

The Banewarrens tops the list (I used it every week for about 8 months), right behind that would have to be the BoEM series, BoVD, Magic of Faerun (I also use FRCS quite a bit, it'd probably make the list)