From a list I created for my Korean co-worker who's often stumped by our Tennessean boss' expressions.

Shock
Well that just dills my pickle!
Well, if that don't put pepper in the gumbo!
Well, slap my head and call me silly!
Well tie me to a pig and role me in the mud!
Well tie me to an anthill and fill my ears with jam!
Bless your heart! (said to someone under duress)
Bless my heart! (said to alleviate personal duress)
Holy bow legged Sara!

Similes and Comparisons
That's about as useful as a trap door on a canoe!
You look about as happy as a tick on a fat dog.
Finer than frog hair split four ways.
He’s busier than a one-legged man at a butt kickin contest!
She was so tall if she fell down she would be halfway home. (derision; said sarcastically)
He was as mad as a mule chewing on bumblebees!
You're lyin' like a no-legged dog!
Excuses are like backsides. Everybody's got one and they all stink.
That was faster than green grass through a goose.
You look as happy as a dead pig in the sunshine. (derision; said sarcastically)
Why are you smilin' like a goat in a briar patch?
Our preacher's as full of wind as a corn-eating horse.
They’re off like a herd of turtles. (derision; said sarcastically)
Felt like a duck at a cock fight. (felt out of place)
Smelled like a fart in a gym sock.
Shakin' like a dog shittin' peach pits. (shaking A LOT)
Looks like a sow in a dress. (you can dress her up but you can't take her out)
Well, don't you look prettier than a glob of butter melting on a stack of wheat cakes!
Uglier than homemade sin.

Southern Expressions: Part 1