Which single non-core 3e book do you use the most?

[NiTessine]

The FRCS. Two of the campaigns I currently play in are Forgotten Realms, as were three that I ran before... Magic of Faerûn is the next most used, and Oriental Adventures after that.

 

[Fenes 2]

I most often use Sword and Fist, since the main PCs in my campaigns are melee fighters, and when designing the NPCs I use a couple of the PrCs in that book. (Just last monday I had to create a high-level duelist.).
Most often is somewhat of a misnomer, however, since I seldom use non-core material as a DM, or rather non-core-non-homebrew material.

 

[jemkym]

The Book of Vile Darkness. Apparently I like playing characters with a bit of evil in them, or is that characterising players with a bit of evil in them? The Lords of Evil chapter is superb.

 

[Nathan]

As a DM:

1. Forgotten Realms Campaign Setting
2. Magic Of Faerun
3. Faiths and Pantheons

 

[Buttercup]

Seven Cities (Penumbra) because I'm using two of the communities from that book. I don't actually bring the book to the table, because I've photocopied the maps and typed up the locations for myself.

Creature Collection II would be a close second.

 

[Ukyo the undead]

Creature Collection I & II

 

[Bagpuss]

Creature Collection I & II

I'ld have to say those two as well.

 

[francisca]

As a DM, Everyone Else, by Ambient.

 

[Ruined]

Other than the campaign-specific material (I run Scarred Lands), I've been using the Path books by FFG. Really good material.

And GM Mastery: NPC Essentials by Johnn Four has gotten a lot of mileage as well.

 

[Bendris Noulg]

The single most?

Relics & Rituals.