David Sedaris is tears down your face  funny!

Best humor books I have ever read:

I was told there'd be cake by Sloane Crosley (non-fiction)

Dress your family... David Sedaris (non-fiction)

In a Sunburnt Country by Bill Bryson (non-fiction)

About a Boy by Nick Hornby

Catch 22 by Joseph Heller

Anything by Tom Robbins

Anything by Christopher Moore

The Hit Man (Keller) series by Lawrence Block:  Only 4 in the series, but there are some seriously laugh-out-loud dialogues.  I embarrassed myself on the train, listening to the books on the iPod, more than once!

I have to agree with the recommendations of Pratchett and Evanovich.   

Patrick McManus!!!

He writes outdoor stories about fishing, hunting, camping, etc.  But even if you're not in to those things, you will laugh.  He also tells a lot of "true" stories about growing up poor as a young man in rural Montana.

Look for his collections of short stories, and not his mysteries.  Funny, funny stuff!

i remember "kick me" by paul feig as being very funny, but it's been a few years, so my memory could be failing me. i could not stop laughing for the first half of "walk in the woods" by bill bryson, but that stopped by the second half.

any and all david sedaris! "when you are engulfed in flames" is great, as are "naked" and "me talk pretty one day", however his writing often has a melancholy edge as well. if you're looking for straight up humor, no dark side, then check out his story "the santaland diaries" or his audio reading "david sedaris: live at carnegie hall"

i'm about to begin "bossypants" by tina fey and have high hopes! it's rated very well on goodreads, and i really love tina fey.

Oh! And did anyone mention "A Girl Named Zippy" by Haven Kimmel? Very charming, light hearted memoir with several funny moments.

David Sedaris is definitely not considered clean humor and neither is Christopher Moore, by a long shot. But, Moore is still incredibly hilarious and the cleaner of the two authors; I'd still reocmmend him. His Christmas themed novel, "The Stupidest Christmas" might be a good jumping off point.  

Life and times of the Thunderbolt Kid is funny, especially if you were raising kids in the 50s & 60s.  My kids didn't find as much humor in it as I did but it's all in your perspective, I guess.

I'm going to second (third? fourth?) Christopher Moore. Not only does he write fantastic comedy, but his characters are so wonderfully human that you can't help but feel for him. The language can be a bit salty at times, if that bothers you, but Moore uses it to good effect, and it never feels like he's trying to be "gritty" or "edgy."

I will whole-heartedly recommend Terry Pratchett's Discworld series. I'd start a little later in the series if you haven't ever read them before- Guards! Guards! is a great one start with, as is Going Postal.

And if you're interested in humor that's a little more absurdist, I can't recommend Jasper Fforde enough- especially if you're any kind of a literature nut.

The Year of Living Biblically, by A.J. Jacobs, doesn't sound like a humor book, but it is----that  is, in its own peculiar, not-really-making-fun-of-all- those-goofy-"Thou shalt' and Thou shalt not(s)' way.  I laughed, and so did the fellow I gave the book to after I read it.

I recommend Stormy Weather by Carl Hiaasen, or almost any of his books.

Darynda Jones' (Charley Davidson Series) is a hoot.