A perennial favorite, if that’s how you spell perennial. And if that’s what it means.
Now in beautiful color and surround sound.
http://www.deepthoughtsbyjackhandey.com/
What’s your favorite?
“If trees could scream do you think we would be so cavalier as to cutting them down? Maybe if they screamed all the time for no good reason.”
“If you ever fall off the Sears Tower, just go real limp, because maybe you’ll look like a dummy and people will try to catch you because, hey, free dummy.”
Well, this is the one my kid used in his 8th grade graduation speech a couple years ago:
If I could be a bird, I’d be a Flying Purple People Eater because then people would sing about me and I could fly down and eat them because I hate that song.
I’m partial to
If a child asks you why it is raining, a good thing to say is “God is crying.” When the child asks you why God is crying, a good thing to say is “It’s probably because of something you did.”
And people find my posts questionable. Ha! 
djm
the one on the page that Dale linked to that goes
“No Deep Thoughts may be reproduced or posted on websites without permission”
I think the trees one is pretty funny. I think the one about the bum pushing the shopping cart is pretty funny. No wonder you’re a bum! Look at the stupid crap you bought. Or something like that (see, I didn’t actually quote it.)
I must admit that’s my favourite too, not that I’m familiar with very many. I’m on dial-up at home and they each take about five minutes to load.
I know one or two parents who’d say that. Well, actually they’d say ‘It’s probably because of something you did to me.’
Unquestionably… 
“Ask not what your country can do for you, but what you can do for your country!”
I’m partial to this one:
When I die I want to go peacefully in my sleep like my grandpa. Not screaming and yelling like the passengers in his car.
(Something like that.)
And an Emo Phillips corollary
…and always remember the last words of my grandfather, who said “A truck!”
That one has always been my favorite. I quote it more often than I should.
Back when Deep Thoughts were a regular part of SNL I actually bought a book of them. I don’t know what happened to it though…
It’s a toss-up between
I can still recall old Mister Barnslow getting out every morning and nailing a fresh load of tadpoles to the old board of his. Then he’d spin it round and round, like a wheel of fortune, and no matter where it stopped he’d yell out, “Tadpoles! Tadpoles is a winner!” We all thought he was crazy. But then we had some growing up to do.
and
I was taking my little nephew to disneyland, but i decided to play a mean trick. i pulled up next to an old, burned down warehouse. “Oh no,” i said. “Disneyland burned down.” He started crying, and i was about to tell him it was all a joke and drive to the real disneyland, but it was getting kinda late.
Aww! I feel bad just reading that!!!
“Laura objected to my use of the word ‘puke.’ But that’s what her dinner tasted like.”
Contextual advertising shows “Why Me, Lord? A comforting message for vicitms of abuse.”
Yaaaaaaaaaaargh! 
Then there’s:
Marta always talks about sensuality. But, I don’t think Marta would know sensuality if it bit her on the ass.
One I seem to recall coming from Emo, but I’m not certain.
My shrink told me that you can tell a lot about someone’s state of mind by the way they eat their gingerbread men. If you bite off the legs first it means you’re insecure and you want to stop people you depend on from leaving you. If you bite of the arms it means you want to control what people do.
He refused to see me any more, just because I asked what it means when I gouge the eyes out with my teeth…