I like similes that usual animals in their comparisons, as they are extremely visual and often beg some leap of the imagination (it’s easier to picture simile animals as cartoons or drawings, not the National Geographic kind):

as hungry as a bear

as slippery as an eel

as wise as an owl

as blind as a bat

But the best are animal similes that don’t make a sense:

as happy as a clam

as sick as a dog

as healthy as a horse (debatable)

And, my favorite:

as drunk as a skunk