All-time favorite is George Carlin. He had a slow period in the 80s when he was transitioning from laid-back hippy to angry nihilist, but he’s been back on track since the early 90s and his newer stuff is some of the best I’ve ever seen.
Of the younger guys, Dave Chapelle, Dave Attel, and David Cross can’t be beat. Are Davids inherently funny?
And though this wasn’t really the question, Robert Klein’s Child of the Fifties is the funniest single stand-up album ever.
Lenny Bruce.
Sorry for the double post, but I forgot to chime in on Izzard. I like his stand-up OK, but I also think he’s a pretty good actor. He was great as Chaplin in The Cat’s Meow, and when I visited London I saw him in a performance of Lenny and he was much, much better than Dustin Hoffman. I guess he was much more comfortable playing a stand-up than Hoffman ever could be.
Add me to the Eddie Izzard fan list. I think he is just a riot. I love him. I love George Carlin, Lewis Black, Jon Stewart, Billy Connolly (sorry, nitpicky, I know), Brad Sherwood, Drew Carey, the list goes on and on and on. (I’m a HUGE stand up fan.)
I loved MTV’s “Half Hour Comedy Hour”, VH1 “Standup Spotlight”, and most of the comedy specials on Comedy Central.
But it’s probably fitting, since I date a comedian, who I’m REALLY in love with. 
Carlin
I saw Demetri Martin on Comedy Central once, and I thought he was frikkin hilarious. I haven’t been able to find out much about him though, he doesn’t seem to be too popular for some reason. Also I like Brian Regan, and Triumph the Insult Comic Dog. And Steven Wright.
Interesting how no one’s mentioned Dennis Leary.
Oh wait, this is about COMEDIANS!
Steve Martin in the 70’s and early 80’s
Lewis Black, currently:
for the reason posted by* Troy McClure SF***
Whew. I read the entire list and I was getting mighty concerned that no-one had mentioned Steve Martin. But only one vote each for Cosby and Martin? Sigh. Kids today. Go get some of their olde timey comedy albums. You can even play them around your kids or grandparents. Imagine, comedy without obscenity! WOW! (Assuming the easily offended don’t quite understand the joke about “singing from your diapraghm”.)
Not that I am offended by obscenity. Eddie Murphy also was great in his standup days(Wait a minute! No one has picked him yet? Sheesh.) But if I want giggles simply from repeating words society finds distasteful, I’ll teach them to my 6 year old daughter and have her sing them loud and proud at the mall.
And, to be a part of the gang, Izzard is hilarious.
I like Gallagher. I have seen all the shows several times on Comedy Central but I still laugh every time. I like the way he thinks.
Elayne Boosler, Ellen , Brett Butler, Eddie Murphy and Cosby had good routines as well.
Funny.
I have to vote for Eddie Izzard, Bill Hicks, Lewis Black, Mitch Hedberg and David Cross.
In addition, let me mention Ron White, who you might have seen on the Blue Collar Comedy Tour (and movie.)
“Six bouncers hurled me out of a nightclub like I was a Frisbee.”
My favorites are Eddie Izzard (Cake or Death?), David Cross, Robin Williams, Chris Rock, and Richard Pryor. I thought Eddie Murphy was quite funny in his day, as well.
Oh geez. I left out one of my all-time favorites (and am surprised that nobody mentioned him yet):
Buddy Hackett
Although it’s been a while since he was really active, this thread can’t pass into oblivion without a mention of Jonathan Winters who made comedy what it is.
Of the active people, Izzard, Williams, Rock, and Rudner (Rita) are my favorites. Carlin is almost as important as Winters, but Jonathan set a standard so high nobody can really compete.
And Steven Wright is the Gary Larson of stand-up.
I have to sound off for Richard Jeni. I saw a couple of specials of his in the early 90s before that trainwreck, Platypus Man, and boy he was Hi-larious.
That said, I am really enjoying Friday Nite Stand Up on Comedy Central. Some virtually unknown comedians coming up, and some funny, funny guys.
Dane Cook is hilarious especially if you grew up in the 80’s. He has bits on the Kool Aid guy, jelly shoes, and Simon. Plus, if you’re Catholic you’d appreciate his take on Communion - crouton au Christ.
Mitch is so deadpan and insightful that you end up laughing and saying “Hey wait a minute…” I love his baked potato bit and the Pringles/tennis balls connection.
Brian is a goofus. He reenactment of someone walking into a spider’s web makes me laugh until I pee. Plus “Take luck!”
Bob Newhart. Really. My parents told me that Newhart was the really big stand-up comic before Bill Cosby came along. I have their old Newhart albums, and it’s some pretty funny stuff.
Another vote for Sam Kinison too. I still have a tape of the (8th or 9th) Annual HBO Young Comedians Show where I first saw him. He was wild and brilliant! don’t ask is right, the bit about starving people is brutally funny: “…Get your kids, get your shit, we’ll make one trip! We’ll take you to where the FOOD IS!”
Of course I love the comedy stylings of George Carlin and Chris Rock. But have any of you ever seen The Amazing Jonathan? He absolutely cracks me up every time I watch him.
Funniest of the ones I’ve seen live…
Argus Hamilton - funniest polictical humor today, Here’s his site.
Wild Willy Parsons - If you don’t laugh, he’ll beat the crap out of you. Link
Felicia Michaels - I have to mention her because she let me crash at her place between jobs for awhile, plus she’s darn funny. another link
Dom Irrera - Simply Dom!
Steve Oderkirk - Thumb Wars, that’s all.
In the interest of full disclosure, I worked at the Comedy Store years ago.
I second the vote for Bob Newhart and George Carlin
What? you don’t like Joe Piscopo?
I’ll secong Rich Hall and Stephen Wright and throw in Richard Lewis for good measure.
The funniest I’ve ever seen though was Steve Martin in a live performance back in '78. Absolutely hilarious.