As long as we are lumping in songs too.
Never Bite A Married Woman On The Thigh
Crazy. This poem may have been my first exposure to the Great Beyond. I think it used to give me chills.
From Uncle Shelby’s ABZs:
L.
L is for lollipop. Would you like a nice big lollipop?
Go into the kitchen and look under the sinkfor another L-word: “lye.” Pour some of it on the floor and tell Mommy you ate it. (This is a fib or a little white lye.) Mommy will take you to the hospital, and after they pump your stomach they will give you a nice big lollipop!
I also liked his censorship poem, “They’ve Put a Brasseire on the Camel.”
Knock knock.
Who’s there?
Me.
Me who?
Exactly.
Exactly what?
Yes, I have an Exactlywhat on a chain.
You have exactly what on a chain?
Yes.
Yes what?
No, Exactlywhat…
I forget the rest, but it used to leave me in stictches before I discovered that he lifted the whole thing from Abbot and Costello.
Last one:
If I had a Brontosaurus,
I would name him Morris.
But if he suddenly had a bunch of little Brontosauri,
I would name him Lauri.
Mr. Smeds and Mr. Spats.
Pamela Purse yelled “LADIES FIRST!!”
Okay, this is really the last one:
Elmer came to school and said:
“Durn, I growed another head.”
Teacher said “Elmer, it’s time you knowed:
The word is ‘grew’ instead of ‘growed.’”
Insanity.
What can I say? I love Shakespeare. 
http://members.tripod.com/crazcowboy/Silverstein/hamlet.htm – A better link to the poem. (My first one’s a Google cache.)
Listen to the MUSTN’TS, child,
Listen to the DON’TS
Listen to the SHOULDN’TS
The IMPOSSIBLES, the WON’TS
Listen to the NEVER HAVES
Then listen close to me –
Anything can happen, child
ANYTHING can be.