Does "Step on a crack, break your mother's back" count? More a superstition than a saying.
I like the Vermont/New York saying "It's all there", which is said when trying to lift something particularly heavy.
To a pouty child: "That face would make a cow cry."
"Liar, liar, pants on fire" was a common playground taunt.
"Sticks and stones may break my bones/But names will never hurt me."
My wife has introduced "Don't get your knickers in a twist" into the family vocabulary. And of course "Do you have ants in your pants?" for a fidgeter, and "Where's the fire?" to someone rushing along.
About an ugly person: "S/he fell out of the ugly tree and hit every branch coming down."