I’ll freely admit I’m no expert on the genre, but authors I’ve read and loved include:
Raymond Chandler
Dashiell Hammett
Jim Thompson (Pop. 1280 in particular is one of the best novels of any type I’ve ever read)
James M. Cain
The only two recent mystery authors whose output I’ve read much of are Elmore Leonard and Kinky Friedman. Like 'em both, but they don’t quite hold up to the classics above. Friedman in particular; his stories really crack me up, but if you’ve read one you’ve pretty much read 'em all.
I guess this is as good a time as any to mention that The Kinkster recently announced he’s running for Governer of Texas. Should be entertaining.
I’ve only read a couple of things by heavy hitters like Patricia Highsmith, James Ellroy and Ed McBain. The Ripley books left me completely cold, L. A. Confidential I thought was quite good, and it’s been so long since I read McBain that I can’t remember what it might have been.
Can’t think of any mystery writers I outright despise except Carl Hiassen. My apologies, I know lots of folks like his stuff, but none of what he seems to intend as humor comes off the least bit funny to me.
I’ve never bothered to read Agatha Christie; doesn’t sound like her stuff would be the slightest bit interesting.
That’s about it.
I’ve only read a few of his books, but I liked them a fair bit. 
I would definitely read more, he’s just someone I never think to look for when I’m getting books.
It’s not my favourite genre, so I’ve not read enough to categorically state a least favourite, but I do love Hiaasen, Elmore Leonard and Scottish author Chris Brookmyre. I guess I just like my crime laced with a generous portion of very dark humour.
I like Val McDermid.
“A Place of Execution” is fantastic, it was the first of hers that I read, and it’s really brilliant. The rest of her stuff is good, but nothing quite touches that one, in my opinion. In the US, she’s called V.L McDermid, I noticed when I picked up some of her books there.
For people on this side of the Atlantic, she created the Tony Hill/Carol Jordan partnership which has just finished a run on the telly called “The Wire in the Blood”, though she didn’t write all of the stories inthe programmes and they adapted the ones she did write. Hers were the best - the first series, I think - but the books were far, far better than the adaptions, as you might expect. And the programmes suffered, in my view because Robson Green played the lead.
Robson bloody Green?!?!? I know it was his company that produced the series but really, could he not have cast someone more credible than himself?
Did I mention I can’t abide Robson Green? 
I would have included Elmore Leonard in the OP, except that he can be very patchy: some stuff is great, but others feel like he just phones them in. Out Of Sight was fantastic; Maximum Bob was meh. Too inconsistent to be an all tiime favourite.
Good:
Rex Stout
Donald Westlake
Agatha christie
Elizabeth George
PD James
Bleh:
Patricia Cornwell
Barbara Vine
Whoever writes the Alex Delaware novels
I should have also mentioned Greg Rucka as a favorite, for his five Atticus Kodiak novels (or at least the first four).
Do you read his comic’s work? He’s very good.
Oh, definitely. It was Rucka’s work in comics (Whiteout and Whiteout: Melt, Queen and Country, Tangled Web #4, Batman, etc.) that made me seek out his novels. I met the guy at MegaCon (Orlando’s big comic book convention) in 2002, got some comics signed, and he was extremely cool and nice.
If you’re a Jim Thompson fan, you might want to check out Charles Willeford. He became pretty well-known for his eighties series of crime novels featuring the Miami detective Hoke Mosely, and one of them was made into a reasonably decent movie (Miami Blues), but it’s his earlier stuff, his fifties novels, that will blow you away.
Try to find The Black Mass of Brother Springer or High Priest of California. Excellent noir books, each featuring a true sociopath as the protagonist.
There’s Jim Thompson, and then there’s everybody else. For me, the good part of everybody else includes:
[ul]
[li]Charles Willeford[/li][li]Dashiell Hammett[/li][li]James M. Cain[/li][li]Raymond Chandler[/li][/ul]
Not breaking any new ground here, I realize, but the right answer doesn’t stop being right just because someone else got there first.
I came in to mention Michael Connelly, particularly the Harry Bosch series. Too bad Blood Work basically sucked as an adaptation of Connelly’s work. I also like a little of T. Jefferson Parker, John Sanford’s Lucas Davenport series, and Robert B. Parker’s Spenser series. I also agree with much of what’s already been mentioned, and have added a bunch of authors to check out.
Joseph Wambaugh’s books are pretty much classics, as far as I’m concerned.
If you haven’t read him, Michael Gruber is well-worth checking out. His first novel, Tropic of Night, was amazing.
Crap. I should have added Joe R. Lansdale above. His larger body of work surpasses generic boundaries of crime writing, but you’ll find him shelved in your local bookstore in the mystery/crime section. Lansdale’s Hap Collins and Leonard Pine novels are excellent.