I have the following bumper stickers, although they aren’t on my car because my car isn’t worth putting stuff on.
Cthulu Loves You
You’re just jealous because the voices talk to me.
I Ain’t No Hippie - I’m Just a Well-Groomed Mountain-Man!
It’s Not the Principal of the Thing - It’s the Money!
In reply to the ever-so-obnoxiously-superior “car empty in case of Rapture”:
** In case of Rapture, can I have your car?" **
This has a lot of great bumper stickers, including many of the ones mentioned on this thread and also happens to be the site where I stole my sig from.
If We’re Not Supposed To Eat Animals, Why Do They Make Them Out Of Meat? (Personal Fave)
B-I-T-C-H = Boys I’ll Take Charge Here
Never Get Behind A VW Bus! (On a VW bus)
Horn Broken, Watch For Finger
The Moral Majority Is Neither
My Dog Humped The Instructor’s Leg At Obedience School.
quote “Grow your own Dope, plant a man!”
GO HAWKS GO !!!…
and take the Falcons with you.
I’d Kill Flipper for a Tuna Sandwich
Lawyers Eat Their Young
Just Visiting This Planet
“Rehab is for quitters” cracked me up the first time I saw that one.
If you’re agoraphobic, you’d be home by now.
I’m Pro-Lifejacket and I Boat!
I Haven’t Been The Same Since That House Fell On My Sister.
Marching to the Beat of A Different Bagpiper.
Animal Testing Is Wrong. The Animals Get Nervous An Give You Incorrect Answers.
Red Meat Isn’t Bad For You. Fuzzy Green Meat Is Bad For You. (I originally had this in “worst”, but the more I think about it…)
Paradigm Shift Happens.
Born-Again Reincarnationist.
Bad cop, no donut.
“Support your right to arm bears”
Cthulu Saves! He might get hungry later
Cthulu for President- The Stars Are Right
That reminds me, I’ll have to look for another Cthulu for President packet from Chaosium this year.
Jesus is coming and boy is he pissed
Bad boy, go to my room!
I only LOOK sweet and innocent
We are the people our parents warned us about
He is YOUR god, They are YOUR rules, YOU burn in Hell!
Get a taste for religion, Lick a Witch!
If ignorance is bliss, why aren’t more people happy?
I believe in dragons, good men, and other fantasy creatures
This one is a key chain but it’s the same type of thing
You can fool some of the people all of the time, they’re called men.
From http://www.landoverbaptist.org:
Get Your Ass To Church!!
I like these:
Forget the Jonses, I keep us up with The Simpsons! (becuase we all love The Simpsons, right?)
I wonder how much deeper the ocean would be without sponges.
Your kid may be an honor student, but you are still an idiot.
Hard work has a future payoff. Laziness pays off NOW! (As an official practicing procrastinator, this one is near and dear to my heart.)
Be nice to your kids. They’ll choose your nursing home.
And my personal all-time favourite:
Why use a big word when a diminutive one will suffice?
my fave for years:
“Who are the Grateful Dead, and why do they keep following me?”
Sorry, I didn’t check the rest of the thread to see if this was there, but this one rocks:
Bumper Sticker
It’s your generic bumper sticker. 
Line Dancing : See what happens when cousins breed
Are In and Out Burgers National, or are they local to California (or Southern California)?
In and Out has bumper stickers which they either give away or sell. Said bumper sticker has a logo and says:
“In and Out
Burger”
Most of these bumper stickers I’ve seen, have the “B” and “R” of “Burger” snipped away. 