What d20 books do you find invaluable?

[Sir Elton]

Use all the time:

Occult Lore

Wow. Thank you.

 

[S'mon]

OGL Conan is the only one that's been really inspirational. I refer to my 1e books far more than to most 3e stuff I bought. I do loo at quint Rogue & quint Fighter a fair bit.

 

[Li Shenron]

I don't refer to them all the time but...

- Manual of the Planes

- Faith & Pantheons

- Tome & Blood

 

[Stockdale]

FFG makes the books I use most aside from the core books.

* Spells & Spellcraft (FFG) - hands down the most used book non-core book I own. I've used the familiar rules, construct rules, spells, This is just a great book.
* Sorcery & Steam (FFG) - yep, its got a broken spine. Cool classes, feats, setting.
* School of Evocation (FFG) - The spells get used a lot.

Also used with some frequency, but not every session

* Familiars (Mongoose Publishing) - The alternate familar paths are really nifty
* Arcane Strife (EN Publishing) - Good resource for Wiz Spells.

 

[der_kluge]

... waits to see if anyone lists the book of erotic fantasy...


That's a tough one. d20... d20...

I've gotten a lot of insipration from _Magical Medieval Society: Western Europe_.
I also heavily used _Requiem for a God_ in my last campaign. It's an awesome sourcebook.
I also got a lot of use out of the Book of Templates (DE), which is just awesome.
I find Phil Reed's stuff to have a consistent level of quality. His 101 books are just incredible.
My own Artificer's Handbook is my must-have resource for magic item creation.

I have some other really nice products, but these ones above have probably influenced me the most. At least in my last game. My next campaign might have a different list, but the Phil Reed stuff would probably at least be included to some degree, and maybe MME:WE again. My next game will be HARP, so obviously the usefulness of d20 stuff will be limited.