"It's come a Johnstown flood!"

[billanole]

is how one old boy I used to work with would say it.
My older brother always called it a toad strangler.
Yankee at work is surprised that his neighbor refers to a gully washer.
Rainin' cats and dawgs...
Pouring p.... out of a boot.

A few hours ago, we had a band of rain come through that hit our roof so hard that it sounded "like a cow p... on a flat rock".