Tiger rattlesnake
The Tiger rattlesnake may have a low venom yield but it is still regarded as the most toxic of all rattlesnake venoms. As it does have the highest venom toxicity in the Western Hemisphere. While they tend to be reluctant to bite, tiger rattlensakes are aggressive so keep your distance if you run into one.
Common death adder
Native primarily to Australia, the Common death adder (and boy, what a name that is) contains a high toxic neurotoxin which causes paralysis or even death. It delivers one of the fastest strikes among all other venomous snakes that have been recorded in Australia. If bitten, death occurs within six hours, so best to avoid these buggers.