Bob Hare is a given, although I highly recommend Cleckley's classic "The Mask of Sanity" circa 1941. Although alot of research has been done since that time, the conceptualization of the "Cleckley psychopath" is largely the same. Its an informative and interesting read.
For more modern emprical work, this of course depends on what you want to know. Diagnosistic and taxometric issues, treatments, therapies and outcomes, etiologies, genetics, risk factors? I would look up articles by Lee Robins, Ted Millon (of MCMI fame), Thomas Widiger, Donald Lynam. There is really no sentinel study out there for ASPD.