I would love some nominees so we can settle this burning question once and for all.
Quoth the flupmeister: John Cleese, Bill Cosby, Robin Williams
We all know people who are funny, but I’m really looking for the best of the best of the best. Please do not nominate yourself, or Gallagher. What do youse think?
Are you limiting the question to performers?
Because I think that of all people in the professional comedy field, Dave Barry, the writer, is top of the heap.
If performers only, I’d probably agree with Cleese. Harry Anderson is also very good.
Eddie Izzard, Douglas Adams, John Cleese.
Whoops…that’s pretty damn Anglophilic.
Lemme throw in Steven Wright for good measure.
Eddie Izzard, Rowan Atkinson, George Carlin, Eddie Murphy.
P.J. O’Rourke
Dennis Miller! He, Eddie Izzard, and John Cleese are the comedy Trinity.
The funniest man alive is that bum down the street.
He’s the funniest-smelling man alive, anyway.
I’m going to limit my list to stand-up comedians, since they have the extremely difficult task to presenting their humor to live audiences.
George Carlin, Chris Rock, Paula Poundstone, Eddie Murphy, Dennis Miller, Steven Wright, pre-TV Bill Cosby, pre-Movie Robin Williams, pre-burn unit Richard Pryor.
Eddie Izzard seems to be the comedy Flavor of the Month but has he really been “around” long enough to join the Dennis Millers and the John Cleeses?
My dad is the funniest man alive. Really. Trust me.
Uh, I’m feeling really old now, but, um, could someone tell me who Eddie Izzard is? I’ve never heard of him. (Hanging head.)
Robin Williams. At least, he was the funniest man alive, before he had kids and started doing all those crappy Disney movies and truly horrific dramas. I think we’d all be better off if Robin Williams realized that he’s just not an actor.
I haven’t heard of Eddie Izzard, either. I’ll nominate Peter Schickele (P.D.Q. Bach), although he won’t be well enough known to win. High marks for both writing and performing, and covering several genres well (physical comedy, satire, puns, etc.) If you are a fan or student of classical music and are unfamiliar with him, I recommend listening to some P.D.Q.
Dunno if he’s been “around” long enough–though he’s been doing it for about a decade–but the man makes me laugh harder than I’ve ever laughed in my life.
jodih: Eddie Izzard is a brilliant British comedian who happens to be a transvestite, and he’s got an extremely intelligent sense of humor, deriving his jokes in large part from his interest in and love of history. He’s been described as an amalgamation of Monty Python, Steve Martin, and Richard Pryor. When he performs, he doesn’t go from a written script–it’s basically ninety minutes of stream of consciousness, whichever jokes he remembers and decides to riff on. He’s fantastic. Oh, and he does two impressions–Sean Connery and James Mason. He does them often.
“I was a driven Boy Scout, a very driven Boy Scout. Driven everywhere, I was.”
“I like my coffee hot and strong, like I like my women, hot and…strong. With a spoon in them.”
“When I was in school in the Seventies, the career advisor used to come to our classes and say, ‘I advise you to get a career.’ One day he took me aside and said, ‘What do you want to do, kid? Tell me your dreams!’ And I said, ‘I want to be an astronaut, and fly into outer space and discover planets no one’s ever discovered.’ And he said, ‘Look, you’re British, so scale it down a bit, all right?’ So I said, ‘Well, all right, I want to work in a shoe shop then, and discover shoes that no one’s ever discovered, right there in the back of the shop on the left.’ And he said, ‘Look, you’re British, so scale it down a bit, all right?’ And I said, ‘Then I want to work in a sewer, and discover sewage no one’s ever discovered, and pile it on my head and come to the surface and sell myself to an art gallery.’ And he said, ‘Look, what the fuck have you been smoking, eh? …You certainly haven’t been smoking in a bar in California.’ …'Cause you can’t. Yes, no smoking in bars, and soon no drinking, and no talking. Careful, California. You’re supposed to be the crazy state!”
…Er, sorry. That was a representative sample. 
Damn. Here’s that link.
Think of these as suggestions, because it’s hard to name just one. That and I’m afraid I forgot one that someone else will post and have to beat myself about the head and shoulders for not remembering. These guys usually have me rolling in laughter on a fairly consistent basis:
Dennis Leary, Buddy Hacket (is he still alive), Chris Rock, Cheech & Chong (I’ll consider them one because apart they are useless), old Robin Williams, Drew Carrey (his stand-up was great, that and he’s from the Midwest), Chris Farley (wait, he’s not alive is he).
I’m sure there is a ton of others. But I had to at least mention Dennis Leary.
I really like Eddie Izzard.
I know he’s dead but Bill Hicks was by far the funniest man/woman I’ve ever heard.
I have to second both Dave Barry and P.J. O’Roarke. (Oh, to be able to log in often enough to be first with something…)
For sheer gut-funny, Barry can have me rolling. For scathing yet insightful political/social satire, nobody beats O’Roarke. P.J can really turn a phrase. So many times I sit in awe at just how he can put something to point out the absurdity. And he truly is funny.
Ah, yes, Dave Barry. How could I forget thee?
I would like to give honorable to every person who ever wrote an episode of the Simpsons (except, of course, for the one in which Bart shoots the bird with a bb gun, cuz it sucked, and the one where Skinner revealed he was actually “Armon Tamzarian”. Cuz it sucked).
Robin Williams is probably the best actor, comedy, drama, or otherwise, alive today. Or one of them. Sorry. Meanwhile, it seems John Cleese has a bit of an edge over the rest, and with good reason. I realized when I saw “The World is NOt Enough” that he is simply hilarious. When he is introduced as Q’s protege R, before he even does anything, or says anything, he simply appears on screen with that huge grin under that moustache (that, had you not already known it, would have screamed, BRITISH!!!), and the moment he appeared, I cracked up. And I don’t know why.
Can’t believe I forgot Carlin. Too bad I’d be breaking my own rules to nominate my dog…
Oh yeah, what about Mel Brooks?!!!
Kurt Vonnegut, Jr.
I would agree with Dave Barry and Bill Hicks, may he rest in peace.
I would nominate David Allen Greir. Not for any of his film work, but for his interviews and game show appearences.
Alpha brought up a good point—I think the funniest men alive right now are women! Paula Poundstone, Margaret Cho, Jennifer Saunders, sometimes Judy Tenuta.
I am allergic to Jim Carrey, Billy Crystal, Robin Williams. I’m sure they are sterling gentlemen in their private lives, but I find them about as funny as a crutch.