These poison rules are made to make poison much more realistically deadly. Really deadly!!! They are geared to a less heroic, grim and gritty type game. So try to gauge whether they are right for your gaming group.
The poisons are listed by delivery method (swallowed, injected/blade venom, contact). They are also divided into groups of Common, Less Common, Somewhat Rare, Rare, Very Rare and Exotic. These categories refer to the difficulty in brewing the poison; shown below. Some delivery methods do not have Common types.

Common poisons require only a Rank of 1+ to make.
Less Common require a Rank of 9+ to make.
Somewhat Rare requires 12+ Ranks to create.
Rare requires 15+ Ranks to make.
Very Rare needs a Rank of 18+ to brew.
Exotic poisons require 20+ Ranks to create.

Availability refers to the chance that a given poison will be available from a particular individual, who must still have been able to make the poison in question in the first place.

Prices are given in silver pieces ("s") because Domibia uses silver as the primary currency. I don't feel like going in and changing every damned "s" to a "g", so just treat them as gold pieces...

***DISCLAIMER*** I swiped this stuff from an old copy of Different Worlds magazine a long time ago and converted it to GURPS, what I have posted below is my d20 version of the GURPS conversion of the original article, which I no longer have available in order to give proper credit. If you know who the author is, please let me know, so that I know who I am ripping off...

Update 2008: I found out! I got it from "Poison: The Cup of Death", by Larry DiTillio, Issue #31, pg 8-15
Thanks to Steve Brooks who told me back in 2006 but I didn't have my admin account set to forward mail. Ooops!

Common Swallowed Poisons

Name: Metal Salt	Form: Grey powder. No color when mixed. Tastes slightly bitter and metallic.	Availability: 50%
Begins Effect: 1d8 minutes		Rank Needed to Make: 1+
Runs Course: 2d20 minutes	Symptoms: Increasing shortness of breath, dry and bitter taste in throat, slight reddening of the eyes.
Damage: 5d4 flat
Dose: 1/2 gram
Price: 30s
Base: Mineral	Saving Roll: DC 8. A successful save will reduce damage by 1/2.
Odor: None

Name: Blood Vinegar	Form: Light red liquid or tablet. Tastes vinegary. Adds a slight reddish tint when mixed.	Availability: 75%
Begins Effect: 1d10 minutes		Rank Needed to Make: 1+
Runs Course: 3d10 minutes	Symptoms: Swelling of fingers, ache in temples, nausea. May cause reduced manual dexterity, -2 to use hands.
Damage: 3d6 flat
Dose: 1 gram
Price: 45s
Base: Plant	Saving Roll: DC 9. A successful save will reduce damage by 1/2.
Odor: Slightly vinegary

Name: Lung-Burn	Form: Syrupy dark liquid. No color when mixed. Tasteless.	Availability: 50%
Begins Effect: 1d6 minutes		Rank Needed to Make: 1+
Runs Course: 1d8 minutes	Symptoms: Shortness of breath, burning sensation in chest and lungs, tingling of extremities.
Damage: 1d3 per minute
Dose: 1/2 gram
Price: 225s
Base: Plant	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: None

Name: Fever Honey	Form: Green gel. No color when mixed. Tastes slightly sweet.	Availability: 75%
Begins Effect: 2d6 minutes		Rank Needed to Make: 1+
Runs Course: 4d6 hours	Symptoms: Feverish feeling, hazing of vision.
Damage: 4d6 flat
Dose: 2 grams
Price: 75s
Base: Animal	Saving Roll: DC 11. A successful save will reduce damage by 1/2.
Odor: Flowery-sweet

Name: Spider Berry	Form: Wine-colored liquid. No color when mixed. Tastes somewhat like blueberries.	Availability: 10%
Begins Effect: 1d20 seconds		Rank Needed to Make: 1+
Runs Course: 3d10 minutes	Symptoms: Partial paralysis of all limbs, numbing of lips and tongue, slight swelling of throat glands.
Damage: (1d3 / 2) per minute
Dose: 1 gram
Price: 300s
Base: Plant	Saving Roll: DC 12. A successful save will reduce damage by 1/2.
Odor: None

Name: Hack Lemon	Form: Off-white powder with black specks. Tastes like lemon. No color when mixed.	Availability: 75%
Begins Effect: 1d4 minutes		Rank Needed to Make: 1+
Runs Course: 1d20 minutes	Symptoms: Violent coughing, shortness of breath.
Damage: 5d2 flat
Dose: 1 gram
Price: 30s
Base: Mineral	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Lemony

Less Common Swallowed Poisons

Name: Silent Death	Form: Clear liquid. Tastes slightly salty, darkens color of whatever it is mixed with.	Availability: 50%
Begins Effect: 1d10 minutes		Rank Needed to Make: 9+
Runs Course: 5d10 minutes	Symptoms: Hot and cold flashes. Paralysis of vocal cords within first five minutes of effect.
Damage: 1d3 per minute
Dose: 1/2 gram
Price: 150s
Base: Plant	Saving Roll: DC 13. A successful save will reduce damage by 1/2.
Odor: None

Name: Boreweed	Form: Crushed brownish leaf. Tastes "planty" like lettuce. Leaf does not dissolve in liquid.	Availability: 50%
Begins Effect: 3d6 minutes		Rank Needed to Make: 9+
Runs Course: 1d4 hours	Symptoms: Violent headaches, pain makes concentration almost impossible. Can cause brain damage, lose 1 Int or Wis for every 12 points of damage taken (roll randomly)
Damage: 5d6 flat
Dose: 1 gram
Price: 300s
Base: Plant	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Herbal scent

Name: Iron Ale	Form: Light, amber liquid. Tastes like ale with a slight metallic aftertaste. Will color lighter substances.	Availability: 75%
Begins Effect: 5d6 minutes		Rank Needed to Make: 9+
Runs Course: 3d8 minutes	Symptoms: Nausea, stomach pain, vomiting.
Damage: 1d6 per minute
Dose: 2 gram
Price: 375s
Base: Mineral	Saving Roll: DC 12. A successful save will reduce damage by 1/2.
Odor: Dried beer

Name: Silverfish	Form: Silvery oil. Fishy taste. No color when mixed.	Availability: 10%
Begins Effect: 1d8 minutes	Form: Silvery oil. Fishy taste. No color when mixed.	Rank Needed to Make: 9+
Runs Course: 5d6 minutes	Symptoms: Shortness of breath, loss of equilibrium, pain in lower back.
Damage: 1d2 per minute
Dose: 1/2 gram
Price: 225s
Base: Animal	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Slightly fishy

Name: Gutfire	Form: Small yellowish tablet. Dissolves almost instantly in liquid. Colorless and odorless.	Availability: 50%
Begins Effect: 1d6 hours		Rank Needed to Make: 9+
Runs Course: 2d6 hours	Symptoms: Seems like ptomaine: nausea, stomach pains, sweating.
Damage: 1d10 per hour
Dose: 1/2 gram
Price: 525s
Base: Plant	Saving Roll: DC 13. A successful save will reduce damage by 1/2.
Odor: None

Name: Green Lotus	Form: Greenish powder. Gives a slightly melony taste and greenish tinge to whatever it is mixed with.	Availability: 10%
Begins Effect: 1d4 minutes		Rank Needed to Make: 9+
Runs Course: 2d8 minutes	Symptoms: Twitching of limbs, blurring of vision, slurring of speech.
Damage: 4d6 flat
Dose: 1 gram
Price: 750s
Base: Plant	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Honeydew melon

Somewhat Rare Swallowed Poisons

Name: Skintwister	Form: Blue powder. Dissolves instantly in liquid, slight blue color, no taste.	Availability: 10%
Begins Effect: 1d10 minutes		Rank Needed to Make: 12+
Runs Course: 1d20 minutes	Symptoms: Victim is thrown into violent convulsions and suffers great pain. Walking is impossible.
Damage: 2 1/2 pts per minute
Dose: 1/4 gram
Price: 1200s
Base: Animal	Saving Roll: DC 15. If save is made the victim will still take 1/2 damage, but will be able to walk and keep the convulsions down to frequent shakes.
Odor: None

Name: Jasmine Seed	Form: Clear liquid. Tasteless and colorless.	Availability: 50%
Begins Effect: 1d6 minutes	Form: Clear liquid. Tasteless and colorless.	Rank Needed to Make: 12+
Runs Course: 1d4 hours	Symptoms: Burning sensation in chest and lungs, shortness of breath.
Damage: 5d8 flat
Dose: 1 gram
Price: 900s
Base: Plant	Saving Roll: DC 13. A successful save will reduce damage by 1/2.
Odor: Jasmine scent

Name: Amber Lotus	Form: Dried, reddish-brown leaves. Slight brown color to whatever it is added to. Can be spotted. Tastes sweet.	Availability: 10%
Begins Effect: 1d12 minutes		Rank Needed to Make: 12+
Runs Course: 1d6 hours	Symptoms: Shortness of breath, loss of sensation in fingers, pain in joints.
Damage: 5d3 per hour
Dose: 2 gram
Price: 1500s
Base: Plant	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Cinnamon smell

Name: Snake Marrow	Form: Silvery-white powder, dissolves instantly in liquid. No color or taste.	Availability: 75%
Begins Effect: 1d4 minutes		Rank Needed to Make: 12+
Runs Course: 3d20 minutes	Symptoms: Chills, fever, shaking, blurring of vision.
Damage: 5d6 flat
Dose: 1/2 gram
Price: 825s
Base: Animal	Saving Roll: DC 12. Poison does no damage if save is made, but will still cause symptoms.
Odor: None

Name: Hell Wax	Form: Black gel, dissolves slowly in liquid, darkening the color of whatever it is mixed with. Tastes rubbery.	Availability: 50%
Begins Effect: 1d4 hours		Rank Needed to Make: 12+
Runs Course: 1d20 hours	Symptoms: Like having a cold; stuffed head, aching muscles, congested throat and chest.
Damage: 5 pts per hour
Dose: 1 gram
Price: 2250s
Base: Mineral	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Waxy odor

Name: Dead Tongue Nut	Form: White tablet with purple specks. Dissolves instantly in liquid. Slightly nutty taste with no color.	Availability: 50%
Begins Effect: 2d20 minutes		Rank Needed to Make: 12+
Runs Course: 4d20 minutes	Symptoms: Loss of sense of taste and smell, pain in ears like a bad earache.
Damage: 5d5 flat
Dose: 1/2 gram
Price: 1125s
Base: Plant	Saving Roll: DC 14. A successful save will reduce damage by 1/2.
Odor: Smells like roast nuts

Rare Swallowed Poisons

Name: Red Lady	Form: Reddish powder. Dissolves instantly, gives a pale red tint to what it is mixed with. Tastes rather salty.	Availability: 10%
Begins Effect: 6d20 seconds		Rank Needed to Make: 15+
Runs Course: 3d10 minutes	Symptoms: Gradual paralysis, chills, blurring of vision in final stages.
Damage: 7 pts per minute
Dose: 1/4 gram
Price: 3750s
Base: Plant	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Slight strawberry scent

Name: Fat Hand	Form: Either light green liquid or a speckled green powder. Tastes chalky and tints lighter liquid green.	Availability: 50%
Begins Effect: 1d6 minutes		Rank Needed to Make: 15+
Runs Course: 3d10 minutes	Symptoms: Tightening of chest, pain in hands and feet, slight swelling of extremities.
Damage: 5d6 flat
Dose: 1 gram
Price: 4500s
Base: Mineral	Saving Roll: DC 15. A successful save will reduce damage by 1/2.
Odor: None

Name: Headsplitter	Form: Grey tablet. Dissolves slowly in liquid (1d6+6 minutes) but has no color. Slight sour taste.	Availability: 10%
Begins Effect: 1d8 hours		Rank Needed to Make: 15+
Runs Course: 2d20 hours	Symptoms: Gradual pain in head, building as more damage is taken. Very violent head pain just before death.
Damage: 2d6 per hour
Dose: 2 gram
Price: 3000s
Base: Animal	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Sour grape odor

Name: Wolf's Breath	Form: Brownish powder. Dissolves very fast in liquid, no taste or color	Availability: 50%
Begins Effect: 3d8 seconds		Rank Needed to Make: 15+
Runs Course: 1d10 minutes	Symptoms: Speeding of metabolism, heavy sweating, shakes.
Damage: 4d8 flat
Dose: 1/2 gram
Price: 2250s
Base: Plant	Saving Roll: DC 16. A successful save will reduce damage by 1/2.
Odor: None

Name: Star Seeker	Form: Light gold liquid, yellow tablet or yellowish powder. Dissolves instantly with no color or taste.	Availability: 10%
Begins Effect: 3d10 minutes		Rank Needed to Make: 15+
Runs Course: 1d4 hours	Symptoms: Hot flashes, "sparkly" vision, dryness in mouth and throat.
Damage: 2d10 per hour
Dose: 1 gram
Price: 5250s
Base: Mineral	Saving Roll: None, but a natural 20 will reduce damage by 1/2.
Odor: Spicy smell

Name: Scarlet Lotus	Form: Crimson leaf. Does not add color, but does add a spicy pepper-like taste. The leaf does not dissolve.	Availability: 10%
Begins Effect: 1d8 minutes		Rank Needed to Make: 15+
Runs Course: 3d20 minutes	Symptoms: Drowsiness that increases with damage. Will fall asleep after taking 1/2 Con in damage.
Damage: 5d6 flat
Dose: 1 gram
Price: 3000s
Base: Plant	Saving Roll: DC 16. A successful save will reduce damage by 1/2.
Odor: Tulip smell

Very Rare Swallowed Poisons

Name: Cold Summer	Form: Light orange powder. Adds no color and dissolves rapidly. Tastes somewhat like gin.	Availability: 10%
Begins Effect: 1d8 seconds		Rank Needed to Make: 18+
Runs Course: 1d10 minutes	Symptoms: Alternating hot and cold flashes, shortness of breath, vomiting.