I would like a list that ranks most poisonous substances in the world
in along with the lethal adult dosage. For example, using google
search I found this tidbit: "The lethal dose of arsenic for a 150
pound adult is 200 mg., for strychnine 75 mg., but for nicotine only
60 mg." I would like a more complete list that includes the *most*
lethal known substance.

Here's a short list: http://chemistry.about.com/cs/5/f/blpoison.htm