A few LD50 (Lethal dose for 50% of the population studied) values:
Alcohol (Ethyl Alcohol): 10.6 g/kg, young rats, orally
Antifreeze (ethylene glycol) 6.86 g/kg, rats, orally
Table salt (sodium chloride) 3.75 g/kg, rats, orally
Marijuana (delta1-3,4-trans-tetrahydrocannabinol) 3.75 g/kg, rats, orally
GHB (Gamma-Hydroxybutyrate, as sodium-GHB) 2 g/kg, rats, intraperitoneal
Wormwood (thujone, one of the main constituent of absinth) 0.45 g/kg, mice, orally
Chocolate (theobromine by itself, although chocolate also contains caffeine) 0.310 g/kg, rats, orally (much higher for cats and dogs)
Ketamine (2-(2-Chlorophenyl)-2-(methylamino)cyclohexanone) 0.229 g/kg, rats, orally
Ecstasy (MDMA): 0.049 g/kg, rats, intra peritoneal
Psychoactive Amanitas (Muscimol): 0.045 g/kg, rats, orally
LSD-25 (lysergic acid diethylamide): 0.0165 g/kg, rats, intravenous
Strychnos seeds (brucine) 0.001 g/kg, rats, orally
Nicotine (3-(1-methyl-2-pyrrolidinyl)pyridine) 0.0003 g/kg, mice, orally
Ricin (a high molecular weight protein made from castor beans, it has been used in experimental treatments for cancer and AIDS) 0.000005 g/kg, mice, orally
Enya (new age female Celtic bard): 0.0 g/kg (instant death), rats and human alike, aurally
(compiled from miscellaneous sources, including Erowid and the Registry of Toxic Effects of Chemical Substances (RTECS)...
A few comments and personal conclusions from this list:
You should not drink antifreeze.
You should not try to assess the accuracy of these data by trying with your dog/cat/goldfish/neighbourhood rat population/significant other/kids. Unless you are scientifically qualified to conduct this type of experiment.
From looking at this list, it should be pretty obvious that LD50 values are to be taken with a huge grain of salt (although no more than 3.75 g/kg if you are an adult-size lab rat): I think we all know that chances to die from a GHB overdose are much higher than from a chocolate overdose, despite appearances of the contrary. The nuance between toxicity and lethality plays a large role in these discrepancies, as well as the essential difference in metabolism between a small rodent (known for thriving amidst major city's most toxic areas) and a much larger biped (also known for thriving in said cities, right next to said toxic areas, but that's not a reason).
Despite my best efforts to harmonize the data (trying to pick preferably oral administration on male adult rats), I was not always able to find perfectly matching data due to lack of source or nature of substance involved (rats will eat about anything, but there is a limit).
Although LD50 experiments altogether are a much controversial issue, due to its particularly inhuman and cruel aspect, the use of Enya's music should decently be banned from any self-respecting scientist's laboratory.