I’ll just mention two books that have caused me to laugh out loud in public, and which contain what I consider to be ‘killer’ gags.
Story Of My Life by Jay McInnerny.
The Gun Seller by Hugh Laurie.
Of course I will **Octavia Smythe-Bunion ** 
My vacation officially started today at 7:00pm. I’m going to spend the next week reading in bed. Tomorrow I’m going to my local Barnes & Nobel to pick up some books that I hope will bring a smile to my face, perhaps a chuckle as well. Quite frankly I’ve been working too many hours this year, talking to too many cranks (oops, I mean customers).
I’ve read most of the suggested titles, but there’s a few that I’ve missed over the years. I haven’t read anything written by John Kennedy Toole or Tom Robbins.
As a side note, I rarely laugh out loud at something I’ve read (chuckles and giggles yes, loud guffaws no) but reading David Sedaris’ Big Boy almost gave me a hernia!
Ben
The Intercontinental Union of Disgusting Characters.
(Of course, none of the humor will make any sense to you unless you’re well-versed in the Advanced Dungeons & Dragons rules, but still…)
Haven’t read that, but it reminds me-- Stephen Fry is a very funny fellow. Making History is pretty good, Hippopotamus is a hoot, and The Liar is freaking brilliant. Don’t bother if the phrase “my back-pussy was like a wind-sock” makes you uncomfortable, however.
I like Making History because a large portion of it is set in the States, so we get to see North American school-life through an aging English school-boy’s eyes. (Although it’s an alternate universe US, so Mr. Fry has an easy out if he slips up on the details.)
The one thing that I came away with from The Liar with is a somewhat difficult-to-explain tendency to smile whenever I see toast. Which isn’t a bad thing, I guess.
Fans of Stephen Fry can find four episodes of his radio program, Saturday Night Fry in the “Personal Pages” section of my webpage. Yeah, Hugh Laurie’s there too, the toady little wanker.
For some “old-fashioned” humor, I’d say:
John Dickson Carr [aka Carter Dickson]
He was an American golden age, mystery writer.
Especially: “The Blind Barber” & “She died a Lady”
- another P.G.Wodehouse fan, here*
Robertson Davies, espc. “The Deptford Trilogy”
David Lodge, espc. “Therapy” or “Thinks”
Both writers I find very insightful and slightly satirical, without being positively cynic. Their book’s are highly entertaining, and I recommend them to anyone who likes to read entertaining, but not brain-dead, novels.
Try going to a used bookstore, or a library, and pulling a sample of the author’s work. Open at random. More with humor than other fiction, I think, you can tell whether you’ll like something with a quick sample. Yesterday I bought a copy of “The Onion: Dispatches from the Tenth Circle” this way.
The difficulty with taking recommendations is that many humorists write within a narrow band of humor styles, i.e., punning, social commentary, satire, parody, and slap-stick are often used largely by themselves. Then there’s “high-brow” and “low-brow”, say the degree to which dirty jokes, dirty language, sex, and bathroom humor are applied. Publications like “Mad Magazine” and “National Lampoon” go for a wide readership by including several kinds of humor, but it’s hard to write all that sort of thing into one, appealing novel style.
Don’t forget to sample: “Bored of the Rings” (Harvard Lampoon), or the books by Spike Milligan about WWII, starting with “Adolf Hitler: My Part in His Downfall”, “Men, an Owner’s Manual”, Stephanie Brush, and the scripts to “Yes, Prime Minister”. Many of “The Goon Show” scripts are available online (Peter Sellars and Spike Milligan). In desperate search for entertainment, I also tried Erma Bombeck and Jean Kerr, and found them readable. And absolutely try Mark Twain and Shakespeare, which have withstood the test of time.
I don’t find Wodehouse’s or Laurie’s writing funny; at least as far as the Americans I happen to know, their perception seems to be flavored by never having lived in England. (I.e., they miss the point of a fair number of the jokes.) For English natives, it’s more: “I know some idiot like that, and I remember when they did something like that!” Not being squarely in either camp, they just don’t grab me.
I’m an American and I think Wodehouse is brilliant, but must be taken in small doses. Despite what his fanatic fans say, he really did write the same story over and over and over. Though the individual lines remain funny, I just can’t read him in big gulps.
That said, if you don’t know the Jeeves books, you just can’t say you know humor.
Alan Coren and Miles Kington are two British pure humorists that I like, but most British humor does, as party_warmer says, rely too much on local references for it to appeal to me.
Here’s an obscure one. David Langford’s The Dragonhiker’s Guide to Battlefield Covenant at Dune’s Edge: Odyssey Two is bar none the best collection of science fiction parodies ever written.
Stephen Potter was a superb writer, famous in Britain and America after the war. His books probably aren’t in print anymore, but I’ve tried to provide a flavour of them in this failed thread.
BTW my pseudonym was a Potter character.
If you’re a technical sort, Neal Stephenson books contain vast amounts of humor. I know that his books aren’t considered “funny”, exactly, but I laugh out loud every time I read the pizza-delivery parts of Snow Crash.
Echoing Exapno’s comment, I think that ANY humor writer needs to be taken in (fairly) short doses. Sitting down and reading three or four books by the same humor author, the humor is bound to pale.
Meanwhile, in addition to all the glorious suggestions above, I would add Janet Evanovich’s series of books about Stephanie Plum, the bounty hunter. One for the money is the first, and the eighth one is just out.
Also, Donald Westlake’s Dancing Aztecs is right up there.
And if you like older stuff, I can’t believe no one has suggested the short stories of Mark Twain or O Henry… or G K Chesterton’s The Man Who Was Thursday
Ephraim Kishon. Greene’s Our Man in Havana.
‘Inconceivable’ by Ben Elton. He has written several other LOL boosk, but they are all founded on politics that occasionally ovwerpowers the humour, and the ending of Gridlock is downright depressing.
‘The Godfather’ or ‘the Househusband’ by Owen Whittaker. Very funny, sensitive writer, in the Nick Hornby school of humour. Also he’s my uncle. 
Then of course Nick Hornby. His latest, ‘How to be Good,’ really made me think.
If you haven’t read every single book by Douglas Adams then you haven’t lived. The Dirk Gently books (‘Dirk Gently’s holistic detective agency’ and ‘the long dark teatime of the soul’) are more mature and less manic than H2G2, but just as funny.
Also, if you like Douglas Adams, try early Tom Holt books. ‘Expecting Someone Taller’ is the first one that springs to mind. He’s one of those writers you definitely don’t read too many of in one go though, because with the recurring themes and obsessions, you start to feel like you’re intruding into some dark part of his psyche where you just don’t want to go. In small doses, he’s pretty funny.
Film scripts are often funnier than the filmms themselves, and you can even get them online.
Your week off reading books sounds like a bibliophile’s heaven. Sigh.
A Confederacy of Dunces
I’ll second anything by Dave Barry
Also, anything by Cynthia Heimel with the exception of her latest, “Advanced Sex Tips for Girls” (Unreadable trash).
Also, Al Franken’s latest book, “Oh, the Things I Know.”
I get a kick out of Penn and Teller’s books, too.
I can’t tell you how happy I am that nobody has mentioned all the 1001 instant books by tv comedians that have been clogging the humor shelves over the past few years.
What a waste of paper those have been.
(Although Bill Maher’s novel, True Story, written before he became so obnoxious, is actually quite good.)
**Pure Drivel ** by Steve Martin. ( I bought this based on the Acknowledgement section. I was pissing myself in the humor section. Right book, right time. Read it in a few hours.
**Holidays in Hell ** P.J. O Rourke. (Actually, any thing by him. But I love his writing.) “Nothing cures communism like a Big Mac.” and " Everyone wants to save the world but no one wants to help mom with the dishes."
If you try PJ, and like him, I second, **Joe Queenan **. The way he pokes fun at pop culture and his vicious wit is very satisfying.
He alone elucidated what I could never put to words in a cohesive manner, aimed at Hollywood, “Where have all the bad guys gone?” and the lackluster villians in the last dozen years.
Someone already mentioned Spike Milligan, but if you like Monty Python-esque humor, read his classic, Puckoon.
I just read MASH* by Richard Hooker. Very funny, with a different tone from the movie and especially from the TV series. Also very short, you can knock it out in an afternoon or less. “Goddamn nail holes.”
Jean Shepard’s writing at it’s best is great fun, although his storytelling is a little uneven. But his stories read so quick that if you don’t like one, you can finish it and move on to a better one quickly.
Eat The Rich by PJ O’Rourke is very funny as well as an interesting take on economics. But if you’re not careful you may learn something before you’re through, to steal a phrase from Bill Cosby.
Anything by Dave Barry.
Anything by Lewis Grizzard.
I can’t believe no one’s suggested Dorothy Parker (especially the collected theater reviews). I find her short stories hilarious as well, but then, I’m a bit morbid.