Here’s one that I found very funny but at the same time rather deep and moving- so it’s a bit of everything. Definitely witty.
A Heartbreaking Work of Staggering Genius by Dave Eggers.
You know, I’ve read everything else by Betty McDonald, but not these. I highly recommend “The Egg and I,” “The White Plaque,” “Anybody Can Do Anything,” and “Onions in the Stew” which are all about Betty’s life and are absolutely hilarious. I have reread them many times.
I also enjoy Florence King’s “Confessions of a Failed Southen Lady.” Some of her other stuff is very funny, too, but she can be a bit too acerbic in her more political stuff.
“House of God” by Samuel Shem is terrific.
A third vote for Good Omens, the funniest book I have ever read. 
Three votes for that, huh. I might have to pick that one up.
This isn’t a book, either, but I like it more than Twain’s comments about Cooper’s manifold sins.
Ok I know we’re not talking about short stories but I just wanted to say…David Sedaris’ collections of stories always make me howl - I wish he would write a novel!
Try it? I read the entire series! 
Though I have to say, the novels were rather thin and don’t really stick with you very well. “Q-In-Law,” OTOH, is timeless, especially if you can visualize John DeLance doing the Q parts…
Yanno, since it’s not available in a US edition yet, I can’t get my library to consider it, and I can’t afford it. 8-\ You’re a meaniehead! 
I’ll heartily third:
My Family and other Animals…the sequel is pretty good too Hedgehogs and Relatives or whatever it’s called
Cold Comfort Farm…has anyone ever found the sequel? It’s out of print, apparently
My Family and Hard times by James Thurber…dear god, the stories with his grandparents have me gasping for air
I also love love love ALL of the Lucia books by E.F. Benson. Pure delight.
There’s another set of books…Love in a Cold Climate that I found quite amusing and in terms of black comedy I love this one book set in New Orleans about this obese guy…it’s pretty famous…Ignatius Reilly is the character’s name but for the life of me I can’t remember the title.
You don’t have to visualize it. John de Lancie reads the audiobook, as I recall. It’s abridged, and so is even shorter than the book, but he’s brilliant as ever.
In the same vein, “I, Q” (also read by de Lancie) and “Spock vs Q” (de Lancie and Nimoy together!) are extremely funny and enjoyable audiobooks. Short, but great.
Any Tim Dorsey book. My two favorites are Florida Roadkill and The Stingray Shuffle.
Anything by Dorsey is going to blood-splattered and hilarious.
That was in my OP, actually. It’s called Confederacy of Dunces; Peter Kennedy Toole is the brain behind it. Definately a top-fiver.
The second page and nobody’s mentioned George MacDonald Fraser yet? (At least I don’t think so.) Get any of his Flashman books. Or, if you can find a copy, read The Pyrates.
And I’ve mentioned this several times before, but Thank You for Smoking by Christopher Buckley is one of the funniest books I’ve read.
I know a lot of of people that turn their nose up on romances, but there are some really good ones out there.
Barbara Metzger is one of the funniest romance writers I’ve found. She writes about the regency period (think Jane Austen). Avoid the full length novels - her sense of humor and writing works better in the regency (novella-size) format.
Her absolute best novel is A Loyal Companion. However, I’ve yet to read one of hers that doesn’t get me giggling.
Although - good luck on finding her regencies. Most people who buy her books keep them. I almost never see one of hers in the used book stores.
Many apologies to Bob - that was me talking, not him. :smack:
The funniest book I’ve read in quite some time was Attaboy Sam! by Lois Lowry. Yeah, it’s a kids’ book. And I literally laughed so hard I peed my pants and got a major case of the hiccups. (And you can hear one of my hiccups in the next block, trust me.)
And Anguished English (is that by Lederer?) also had me rolling in hysterical laughter, but that’s not a novel. But it is incredibly funny.
Burroughs also wrote a hilarious (and very light, 3 hour planeflight read) novel, Sellevision . It’s set at a QVC style shopping channel where a popular host accidentally exposes himself while surrounded by kids in a Christmas special and, well, hilarity ensues. (Gotta love any novel where Joyce Dewitt is a character.)
Speaking of Running with Scissors, its cast is set.
David Sedaris is one of my favs and I snatched up his newest book. Turns out he edited a collection of short stories. Darn! They look to be good stories though.
Lamb is C. Moore’s best, I agree with silenus. Bloodsucking Fiends is a good second.
The Diaries of Adam and Eve by M. Twain is one of my favorites. Funny and touching as well.
For goofy funny, you might like Laurie Notaro. Her first was Idiot Girls’ Action-Adventure Club. They’re short stories/essays on a theme.
Bailey White’s Mama Makes up Her Mind, among others is good. Essay collection as well, though.
Anything by Gerald Durrell is good, but the books from his family’s years in Corfu are a riot. My Family and Other Animals, which has been mentioned, is the first.
At least as good. My favorite is the Lust Lizard of Meloncoly cove.