The key difference, writes blogger Jason Bittel, is in the biting. Venomous animals internally create a toxin and then inject it into prey or foes. Poisonous animals usually secrete their toxins on the outside.
So here's a rule of thumb: If you are dying because an animal has bitten you, chances are, it was a venomous animal. If you're dying because you touched an animal or (foolishly) put it in your mouth, that's poisonous.
And then, of course, there's the slow loris:
Because the loris manufactures toxin from specialized glands on its elbows, then transfers that liquid to small, curved teeth for injection, the loris is venomous. Alternately, mother lorises cover their offspring’s fur in the same potion, rendering them poisonous.
Read more about various poisonous and venomous animals at Jason Bittel's blog, Bittel Me This.