*If it needs a setup…
*it ain’t a ONE-liner!
A line in need of a setup is by definition a punchline.
I think people have one-liner confused with one-sentencer. An effective punchline usually is one sentence. An effective one-liner need not be. Example:
"Television is a medium. This is because it is neither rare nor well done."
–attributed to Ernie Kovacs
The buttons I see at science fiction cons are wonderful. They inspire me in writing sig lines. Browse through Nancy’s catalog:
http://www.nancybuttons.com/catalog.cgi?action=browse&
I always love the one-liner from comedian Barry Diamond,
“Can I have a cigarette? I left mine in the machine.”
Just read this one on the site I linked to:
Hee!
That Nancy’s Button’s link is awesome!
Thanks Cal!
…
Norm:
“Women. Can’t live with 'em … Pass the beer nuts.”
Speaking of buttons, that reminds me of one I have.
“God, please save me from your followers”
Yes ! That was the guy !
I saw a good one earlier today on Slashdot in the comments for an article about Apple possibly releasing upgrades to the Powerbook and Powermac lines.
"Why is an mp3 player company releasing computers?"
I don’t like to travel, probably because my father used to beat me with a globe.
-Dave Attell
I love you all. I love you more than life itself, but you’re all fucking mad."
(Ozzy Osbourne, “the Osbournes” television show, 2002)
I laughed my ass off when Ozzy came up with that one. I was waiting for him to wax affectionate - then he tells them they’re fucking crazy. Vintage Ozzy. 
“This is not a book that should be tossed aside lightly. It should be thrown with great force.”
Often ascribed to Dorothy Parker, though I don’t believe there’s any evidence she ever actually said or wrote it.
Another reportedly from Dorothy Parker:
“If all the girls at Yale were laid end to end, I wouldn’t be a bit surprised.”
Exactly the reason I didn’t add any kind of lame SETUP. The one-line is much funnier when it is heard by itself. In fact, I tend to believe that’s how it was created and intended. Two guys walk off an elevator and you hear one of them say “Rectum? It nearly killed 'im,” and you’re left scratching your head the rest of the day, laughing to yourself. To pretend that there is a setup for it just kills the humor.
I would say that’s more of a surreal non-sequitor. Especially since it needs to be read not heard. Or so I gather.
Another one attributed to Dorothy: You can lead a whore to culture, but you can’t make her think.
Not a one-liner, really, but a terrific pun. Parker supposedly fired it off without thinking when someone challenged her to make an interesting sentence using the word horticulture.
I don’t have to walk my dog anymore because I walked him all at once. (Steven Wright)
The difference in Iraq and Vietnam is that Bush knew how to get out of Vietnam.
If God didn’t want us to eat animals then why did he make them out of meat?
I’m hung like Einstein and smart as a horse.
“A woman drove me to drink, and I’ll be a son-of-a-gun but I never even wrote to thank her.”
– W.C. Fields