Making Better Poisons

I recommend taking a gander at Arsenic and Old Lace, a poisoner's handbook written for 3.5 DnD. While the poisons rules were changed alot in the creation of Pathfinder, it will be a handy guild for thinking of things you can make poison out of, their effects, and a relative pricing schema. Whether you want to stun, sicken, nauseate, paralyze, render unconscious/sleeping, slow, exhaust, daze, confuse, blind, induce a disease, render mute, or just suppress the scent ability it will have a poison for you.

These make great jumping off points for discussions with your GM, if nothing else.

Making Poisons Better

The best class for being a master poison maker, is as far as I can tell Alchemist. There are quite a number of class features and alchemical discoveries that make you a great poisoner.

• Celestial Poison lets you poison undead and evil outsiders, despite their inherent immunity to poison.
• Concentrate Poison lets you combine two doses of the same poison to increase the DC by 2 and the duration by 50%.
• Malignant Poison lets you increase a poison's DC by 4, extend it's duration by 2 frequency increments, and removes the onset time entirely.
• Poison Conversion lets you change if a poison is a contact, inhaled, ingested, or injury poison.
• Sticky Poison lets a poison you apply to a weapon stay on it for your int mod number of strikes.

To round this out, you can also get poison bombs, which are loaded with cloud kill effect, and the Poison Touch Grand Discovery to have the spell Poison on hand when ever you need.

A Headband of Vast Intelligence will up your spell save DCs by virtue of raising your INT. Otherwise I don't know of any items that will up your DCs. There are a few feats and racial abilities.