We have two sections: First come the books we are sure were written by Westlake.
In the next section I list some early books which are sometimes attributed to him.


The icon , when present, is a link to one or more cover scans.
Honestly, the Publisher field is here only because it is in the checklist provided by Westlake himself in his web pages. Apparently some books were published by different publisher in the same year. So do not trust me on this ... 

Books
Title Date Publisher As Notes
The Mercenaries apa  The Smashers 1960 Random House Donald Westlake  
Killing Time  apa  Operator 1961 Random House Donald Westlake  
Brother and Sister   1961 Monarch Books Edwin West Sleaze
Campus Doll   1961 Monarch Books Edwin West Sleaze. See Trivia.
Young and Innocent   1961 Monarch Books Edwin West Sleaze
361 1962  Random House Donald Westlake  
The Hunter apa  Point Blank apa  Payback    1962 Pocket Books  Richard Stark  
Strange Affair   1962 Monarch Books Edwin West Sleaze
Elizabeth Taylor    1962 Monarch Books John B. Allan A biography
Killy 1963 Random House Donald Westlake  
The Man With the Getaway Face apa Steel Hit [GB] 1963 Pocket Books  Richard Stark  
The Outfit   1963 Pocket Books  Richard Stark  
The Mourner 1963 Pocket Books  Richard Stark  
The Score apa Killtown [GB] 1963 Pocket Books  Richard Stark  
Pity Him Afterwards    1964  Random House Donald Westlake  
The Fugitive Pigeon 1965  Random House Donald Westlake  
The Jugger    1965 Pocket Books  Richard Stark  
The Busy Body  1966  Random House Donald Westlake  
The Spy in the Ointment 1966  Random House Donald Westlake  
Kinds of Love, Kinds of Death 1966 Random House Tucker Coe  
The Seventh apa  The Split  1966 Pocket Books  Richard Stark  
The Handle apa  Run Lethal [GB] 1966 Pocket Books  Richard Stark  
Anarchaos   1966 Ace Books Curt Clark sf novel - Also in  Tomorrow Crimes
God Save the Mark 1967  Random House Donald Westlake  
The Rare Coin Score   1967  Gold Medal Richard Stark  
The Damsel  1967  MacMillan Richard Stark Alan Grofield
The Green Eagle Score    1967  Gold Medal Richard Stark  
Murder Among Children  1967  Random House Tucker Coe  
Philip 1967 Crowell Donald Westlake Juvenile
Who Stole Sassi Manoon?  1968  Random House Donald Westlake  
The Black Ice Score 1968 Gold Medal Richard Stark  
The Curious Facts Preceding My Execution 1968   Donald Westlake Short stories collection. List here.
Somebody Owes Me Money  1969  Random House Donald Westlake  
Up Your Banners  1969  MacMillan Donald Westlake  
The Sour Lemon Score   1969  Gold Medal Richard Stark  
The Dame    1969  MacMillan Richard Stark Alan Grofield
The Blackbird   1969  MacMillan Richard Stark Alan Grofield
The Hot Rock  1970  Simon & Schuster Donald Westlake Dortmunder
Adios, Scheherazade 1970  Simon & Schuster Donald Westlake  
Wax Apple   1970  Random House Tucker Coe  
A Jade in Aries    1970  Random House Tucker Coe  
Ex officio (hb) apa  Power Play (pb) 1970 M. Evans Timothy J. Culver political novel
I Gave at the Office  1971 Simon & Schuster Donald Westlake  
Lemons Never Lie    1971  World Richard Stark Alan Grofield
Slayground  1971  Random House Richard Stark  
Deadly Edge    1971 Random House Richard Stark  
Bank Shot  1972  Simon & Schuster Donald Westlake Dortmunder
Plunder Squad    1972  Random House Richard Stark  
Cops and Robbers 1972  Simon & Schuster Donald Westlake  
Under an English Heaven    1972 Simon & Schuster Donald Westlake Non-fiction reportage
Don't Lie to Me   1972  Random House Tucker Coe  
Comfort Station 1972   J. Morgan Cunningham Spoof
Gangway (with Brian Garfield) 1973  Simon & Schuster Donald Westlake Western
Help I Am Being Held Prisoner  1974  Simon & Schuster Donald Westlake  
Jimmy the Kid 1974  Simon & Schuster Donald Westlake Dortmunder
Butcher's Moon   1974 Random House Richard Stark  
Brothers Keepers  1975  Simon & Schuster Donald Westlake  
Two Much  1975  Simon & Schuster Donald Westlake  
Dancing Aztecs apa  A New York Dance  1976  Simon & Schuster Donald Westlake  
Enough  (A Travesty & Ordo)  1977  Simon & Schuster Donald Westlake  
Nobody's Perfect   1977 Simon & Schuster Donald Westlake Dortmunder
Castle in the Air 1980  Simon & Schuster Donald Westlake  
Kahawa   1981  Viking Donald Westlake  
Why Me  1983  Viking Donald Westlake Dortmunder
A Likely Story  1984  Penzler Books  Donald Westlake  
Levine 1984   Donald Westlake Short stories collection, Abe Levine. List here.
High Adventure    1985  Mysterious Press Donald Westlake  
Good Behavior    1985  Mysterious Press Donald Westlake Dortmunder
I Know a Trick Worth Two of That 1986   Samuel Holt  
One of Us Is Wrong    1986   Samuel Holt  
High Jinx (with Abby Westlake) 1987 McMillan Donald Westlake Mohonk Mountain House Mystery
Transylvania Station (with Abby Westlake) 1987 McMillan Donald Westlake Mohonk Mountain House Mystery
What I Tell You Three Times Is False    1987   Samuel Holt  
Trust Me on This    1988 Mysterious Press Donald Westlake  
Sacred Monster  1989  Mysterious Press Donald Westlake  
The Fourth Dimension Is Death    1989   Samuel Holt  
Tomorrow's Crimes  1989 Mysterious Press Donald Westlake Short stories collection. List here.
Drowned Hopes  1990  Mysterious Press Donald Westlake Dortmunder
The Perfect Murder 1991   Donald Westlake With J.Hitt, L.Block, S. Caudwell, T.Hillerman & P. Lovesey
Horse Laugh and Other Stories   1990 Eurographica Donald Westlake Short stories collection  - Only 350 copies printed and signed. List here.
Humans  1992 Mysterious Press Donald Westlake  
Don't Ask   1993 Mysterious Press Donald Westlake Dortmunder
Give Till It Hurts   1993 The Mysterious 
Bookshop
Donald Westlake A 12pg. booklet  - Dortmunder - Given as Xmas gift to customers by  The Mysterious Bookshop
Baby, Would I Lie?    1994  Mysterious Press Donald Westlake  
Smoke    1995  Mysterious Press Donald Westlake  
What's the Worst That Could Happen?   1996 Mysterious Press Donald Westlake  Dortmunder
The Ax  1997 Mysterious Press Donald Westlake  
Comeback   1997 Mysterious Press Richard Stark  
Backflash   1998 Mysterious Press Richard Stark  
A Good Story and Other Stories    1999 Five Star Donald Westlake Short stories collection. List here.
Flashfire   2000 Mysterious Press Richard Stark  
The Hook    2000  Mysterious Press Donald Westlake  
Bad News  2001  Mysterious Press Donald Westlake Dortmunder - The fist chapter coincide with the short story Spectacles, apperared on Playboy, May 2001.
Firebreak   2001 Mysterious Press Richard Stark Comeback-Backflash-Flashfire-Firebreak ... humm...
Put a Lid on It   2002 Mysterious Press Donald Westlake  
Breakout   2002 Mysterious Press Richard Stark Date of publication: November 2002.
The Scared Stiff   2002 Carroll & Graf Judson Jack Carmichael Published in November 2003 by Orion(UK) under Westlake name.
Money for Nothing   2003 Mysterious Press Donald Westlake  
The Road to Ruin   2004 Mysterious Press Donald Westlake Dortmunder
Thieves' Dozen    2004 Mysterious Press Donald Westlake Short stories collection, mainly Dortmunder. List here.
Nobody Runs Forever   2004 Mysterious Press Richard Stark  


The other books...

All we know that Westlake wrote in his youth some trash/sleaze/lesbian books. Some of those under the name Edwin West are in the list above, since they appear in the very web site of Westlake and we can be sure enough  about them. Another couple is below (thanks, Ken!).
For what concernes the books written as Alan Marshall  or Sheldon Lord  the plot thickens. Indeed, this pen name was used by several authors (Lawrence Block among them) so attribution is not that easy (but look at the Trivia section below for some hints...)
Beside that, I have the baleful impression that (when in doubt) some booksellers have the tendency to attribute to Westlake all the books by A.Marshall, to help the sales a little.

So what follows is only a partial list of the books that I found a reference to. While I'm not particularly interested in reading or collecting these book, I'll be grateful to receive information about them.

Alan Marshall  and  S.Lord & A.Marshall and Alan Marsh
+ Sally (1959) Midwood 22
+ All My Lovers (1959) Midwood Books #15 
+ Man Hungry (1959) Midwood. See Trivia.
+ The Wife Next Door (1960)
+ All the Girls Were Willing (1960) Midwood
+ Virgin's Summer (1960) Midwood
+ A Girl Called Honey (1960) [By Sheldon Lord & Alan Marshall, allegedly by Block  & Westlake. A dedication reads "This  is for Don Westlake and Larry Block, who introduced us" (courtesy of A. Howard)] Midwood 41.
+ So Willing (1960) [By Sheldon Lord & Alan Marshall] Midwood 48.
+ All About Annette (1960)
+ Pages of Sin (1962) Nightstand Books
+ China Tramp (1962) Midnight Reader (459)
+ The Warped Ones (1962) Original Bedside Book #1211
+ Apprentice Virgin (1962). See Trivia.
+ Sin Drifter (1962) Bedside Book #1218
+ The Cruel Touch (1963) Midwood F259
+ Lust Prowl (1963) Midnight Reader 470
+ Flesh Damned (1964) Sundown Reader #SR505
+ Shame Isle (1964) Piller
+ Passion Doll (1964) Sundown Reader SR 528
+ Bed of Shame (1964)  Idle Hour #405 
+ Sin Hidden (1964) Ember Book #EB 938
+ The Sensualists (1965) Leisure
+ Gutter Boy (1965) Nightstand Books
+ Members of the Club (1965) Idle Hour Books #IH 461
+ Scandal Street (1966)
+ Sinner's Circle (1966) Sundown Reader 601
+ The Scandal Man (1966) Evening Reader #ER 125
+ The Violent Vixen (1966) Sundown Reader 610
+ Tonight's Trade (1967) Companion Book #CB 508
+ Dusky Desire (1967) Companion Book #CB 511
+ Easel Orgy (1967) Nightstand Book #1844
+ Dykes on Bikes (1968) Pleasure Reader #PR148.
+ A Patch Of Lust (1968) Candid Reader #CA 950
+ Swap Meat (1968) Companion Book #CB 585
+ What Girls Will Do
+ Legacy of Lust - Leisure Book LB 501
+ Lust Always Rings Twice - Ember Library 391
+ Call Me Sinner  - Nightstand Book. See Trivia.
+ Professor of Passion  - Companion #540
+ Passion Class [by Alan Marsh] Leisure Book #LB 606
Sheldon Lord

+ Kept  [I've seen this book in both Block's and Westlake's bibliographies....]
+ Pads Are for Passion, Beacon 1961

Edwin West

+ Wild (Zodiac ZB-102)(1962) pbo
+ Campus Lovers (Monarch 334)(1963) pbo