I own a copy of Where the sidewalk ends and also A light in the attic, and even after ten years I still love reading these books.
Silverstein really has a way with words, IMO. But have you heard him talk? His poems are great, but I think his voice is reeeeeally creepy!
I think I started a thread a long while back about my favorite Shel Silverstein poems…lots of great stuff, but my all time fav is still this one:
The Hat
Teddy said it was a hat
So I put it on.
Now Dad is saying
Where the heck’s the toilet plunger gone?
Heh.
One sister for sale!
One sister for sale!
One crying and spying young sister for sale!
We are now 33 and 30, and I still get that quoted at me. Silverstein is great. 
I became a fan through the songs of his covered by Dr. Hook and the Medicine Show. The one album of his that I own, Freakin’ at the Freaker’s Ball, where he sings his own songs and recites poetry is kind of strange, though I do like it. Haven’t read any of his books though.
While verifying the album title online just now, I was reminded that he also wrote A Boy Named Sue.
This site “celebrates” his adult writings and says that “he penned nearly 800 songs for the adult market.”
Oh, that Silverstein. I though you meant Andrew [Dice Clay] Silverstein, who had some great poetry of his own:
Ole Mudda Hubbud
Went tooda cubbud
Ta fetch her old dog a bone.
But when she bent over
Rover took over
Cause he had a bone of his own.
Heh, have you read Uncle Shelby’s ABZs? Definately the funniest not-for-children children’s book ever.
I is for ink.
Ink is black and wet.
Ink is fun.
What can you do with ink?
What rhymes with ink?
“DR—”
Another classic by Shel O’Silverstein was “The Unicorn,” made famous by the Irish Rovers.
He also did a neat, but obscure, song for Tex Ritter called “Comin’ after Jinny.”
And don’t forget “I’m being swallowed by a boa constrictor”!
Silverstein is still one of my favorite poets, and I don’t even know how many of his poems I’ve memorized. I’ve got Where the Sidewalk Ends, A Light in the Attic, and Falling Up all sitting on my bookshelf.
Oh my yes - my son and I love to read his poem books and snuggle. My favourite is Hug O’ War.
(Forget the kid’s name)
thought he’d get
a free bath here
at the launderette.
Round he goes now,
slippy slappy,
looking clean,
but not too happy.
I also love the one about the pet snowball that ran away during the night, after first wetting the bed.
Ahh, fond memories of my youth. In 3rd grade we had an assignment to write a fan letter to an author we liked and I picked him. What I didn’t know was that we weren’t supposed to actually send the letter, just write it! I got a form letter back thanking me for my appreciation or interesting or something.
ahem
Mrs. McTwitter, the babysitter,
I think she’s a little bit crazy.
She thinks a babysitter is
s’posed to sit upon the baby!
and
Sarah Cynthia Sylvia Stout
would not take the garbage out
she’d scour the pots and scrape the pans
(something something) and candy the yams
I wish I remembered all of that one…I remember bits and pieces of other ones. Another favorite is “The Mee Who with an Exactly-What.”
Sarah Cynthia Sylvia Stout is certainly a classic, but my all-time favorite is Sick. Unfortunately it’s not very amenable to memorization; it doesn’t have enough large-scale structure to it.
IIRC, the missing bit from Sara is “scrub the floors and candy…”
And who was that evil little girl that wanted a particular pancake from the middle of the stack?
I bought Falling Up for my nephew when he was 5 or 6 hoping he would like it. To my delight he repeatedly reads the whole thing from back to front (he’s 7 now) and asks people if he can read them some poems!
http://www.banned-width.com/shel/works/smokeoff.html
Shel is a total freak! 
Abe, that rocks.
And let’s not forget that brother Shel wrote the words to that classic Johnny Cash tune “A Boy Named Sue”.
Therefore, Shel is on my cool list for keeps.
LC
Bobby Bare recorded three albums of Shel’s songs in the mid '70s.
And, as always, Silverstein was the man who wrote the lyrics for the classic 70s “piss off the feminists” song, Put Another Log on the Fire.
Dr. Demento could base an entire show just on songs with Silverstein lyrics.
And let’s not forget that he was a prolific cartoonist who’s work frequently appeared in Playboy Magazine.