Actually the most deadliest poison is in a spider that cannot harm you, because it cannot pierce your skin with it's teeth. It goes by the name of "daddy long legs."

Venom from a Troll.

I'm going to go with the venom of the Inland Taipan, which is the most poisonous snake in the world. It's venom is 650 - 850 times more toxic than that of a Western- or Eastern Diamondback (rattlesnake) and a single bite has enough venom to kill 100 adult humans....scary. http://en.wikipedia.org/wiki/Inland_Taipan

Steven Seagal movies.

Botulism bacteria

ricin made from castor bean.

Tetanospasmin, the toxin that causes tetanus, caused by certain anaerobic bacteria.

From what I remember thiopentone only takes 2 seconds to kill and plutonium is the most poisonous per volume.

botox from clostridium botulinum

I would guess the most poisonous substance by weight would be Polonium-210. A few years ago the Russian dissident, Alexander Litvinenko, was killed by Russian agents using approx 0.5 microgram = 0.0005 milligrams Po210. http://www.timesonline.co.uk/tol/news/environment/article5733427.ece More info on the Litvinenko murder here: http://en.wikipedia.org/wiki/Alexander_Litvinenko_poisoning From the World Health Organization: "Po-210 emits alpha particles and is 5,000 times more radioactive than radium. The half-life of Po-210 is 138 days. Alpha radiation delivers a large amount of energy to living cells and can cause considerable damage and cell death. . . . "Health risk of Po-210 "Po-210 represents a radiation hazard only if taken into the body – by inhalation, ingestion, or getting into a wound. This “internal contamination” can cause irradiation of internal organs, which can result in serious medical symptoms or death. The toxicity of Po-210 is much higher than that of cyanides, for example. Nevertheless it does not represent a risk to human health as long as it remains outside the body." http://www.who.int/ionizing_radiation/pub_meet/polonium210/en/index.html