Philip Reed has published a short free PDF called the 'assassins guide to poisons' It's avaiable at
Ronin Arts website. It has a short list of poisons and a few supplementary feats and skills on using poisons. It provides minimal detail but is quite adequate, and free.
Bastion Press's
Pale Designs: A Poisoner's Handbook I believe is the most authortitative work.
Poisons are covered by a number of splattbooks for Rogues and Assassins:
I don't own all of the below, but I believe they all have info on poisosn:
Song and Silence
Traps and Treachery
The Assassin's Handbook
Crimson Contracts