The most poisonous animal is not a snake or a spider. It's a beautiful little frog!
"Most frogs produce skin toxins, but the dart poison frogs from Central and South America are the most potent of all.
The golden poison frog, called terribilis (the terrible), is so toxic that even touching it can be dangerous. A single terribilis contains enough poison to kill 20,000 mice or 10 people. It is probably the most poisonous animal on Earth." (source)
Images sources: Zoltan Takacs.
Phyllobates terribilis, shown below, has enough poison to kill 100 humans (source)
Their poison contains toxins that dull the nerves and produce heart and repiratory (sic.) failure. The skin of an adult P. terribilis has enough batrachotoxin to kill 20,000 mice, or 100 adult humans. Two-tenths of a microgram of batrachotoxin is lethal in the human blood stream and each adult P. terribilis contains nearly 200 micrograms.