Joe Heller's "Catch-22".
 
(plus, like Sharke said...anything by Wodehouse)
 

Another vote for P G Wodehouse.
 
Especiallly if you are not in the mood for it, he can disassemble all manner of righteous indignation with one sentence.

yorolpal
Joe Heller's "Catch-22".

+1 on Catch-22. 
 
Also, consider adding Duluth by Gore Vidal to this list.

Looks like I've got some reading to catch up on!
 
 

Jasper Fforde for me is one of a very few that will genuinely make me laugh out loud.
 
Either 'The Fourth Bear' (my personnal favourite), or the Thursday Next series.
 
Anyone who can start a novel with "My father had a face that could stop a clock.  Literally." has to be on to a winner. 

So.. to me Hiassen is "mildly amusing", PGW (one of my favourites) is "charming and witty" and Pratchett is "comedic and funny".
Anyone who likes Pratchett seriously need to read Tom Sharpe.. his stuff is eye wateringly funny.. his 2 or 3 books written about the Police in south Africa got him "persona non grata" status ..but boy they were so, so fin funny.
 

On the humorous side my favourites are some finnish authors. Laughing through tears or being unsure whether it's OK to laugh or not are my favourite styles of humour.
 
Humour in litterature is very demanding to the translator. It's extremely hard to maintain the hooks of Wodehouse, for example, and you need to master english quite well to enjoy the originals.

Kurt Vonnegut.
 
 
 
 
 
 
So it goes.  

backwoods
Flann O'Brien has some good ones (at swim two birds etc)

Love Flann O' Brien. I think I have just about everything by him. My favourite is The Third Policeman, I never saw the twist coming at the end.
 
The late lamented Iain Banks is great too, if you don't mind very dark humour.

Hi,
 
A couple more ...
 
Leunig ... the Australian cartoonist is fabulous and crazy. Got one of his books.
 
PDQ Bach ... the Autobiography, has some serious cartooning, and at one time I posted here a couple of those images to show the Coffee House Band, what they could have done with their music. Unfortunately, they looked at the staff of notes in the pictures as insulting, and not enjoy it as much as they could have. And the suggestion, of course, was ignored in favor of a radio styled song!
 
I wanted more Dr. Demento kind of songs, but the CHB was not gonna be one!
 
Bonzo Dog Doo Dah Band ... sometimes too intelectual, but some very funny (and very subtle) stuff, courtesy of the late Vivian Stanshall.
 
Comedy wise, I enjoyed Robin Williams rants in the early days, and he was great. Richard Prior's stuff that he did with Redd Fox, with never EVER be released. It was dirty and then some, and today, it would be considered inappropriate and what not. It took everything on, including race, sex, religion and drugs! Still some of the best stuff I ever heard, but it will never be heard or released!
 
(more as I think of it!)