I was recently exploring Mystery/Crime Fiction and I became rather fond of Dashiell Hammett and Jim Thompson.
Dashiell Hammett wrote a fair amount of novels like most of the early American crime novelists, look out for Red Harvest, The Maltese Falcon, And The Thin Man.
Jim Thompson has a large number of novels under his belt, his novels are more gritty and dark, watch out for The Killer Inside Me, Savage Night, Pop. 1280, The Grifters, and The Getaway.
Also look out for Raymond Chandler's The Big Sleep, he's another of the classic crime novelists