Here are a few that make me smile:
They're off like a herd of turtles.
Well don't you look prettier than _____ (fill in the blank)
It's the berries!
It's hotter than a goat's butt in a pepper patch.
Bless my stars.
She's madder than a wet hen.
Don't go barking up the wrong tree.
Even a blind squirrel finds an acorn now and then.
He went off half-cocked.
She went whole hog.
In high cotton.
Well spank my ass and call me Charlie.
Thank my lucky stars.
And if you want to know what I think is the berries:
"Read, read, read. Read everything. See how they do it,
just like a carpenter who works as an apprentice
and studies the master. Read. You'll absorb it. Then write.
If it's good, you'll find out. If it's not, throw it out the window."
-- William Faulkner