The alias Dexter gives the shrink is Sean Ellis, the first name of Patrick Bateman's younger brother as mentioned in American Psycho (2000) and main character of The Rules of Attraction (2002). The last name is that of the author of both original works, Brett Easton Ellis.
When Dexter starts looking into a series of possible murders made to look like suicides, the soundtrack contains the key motif from Brecht/Weill's Ballad of Mack the Knife from The Threepenny Opera.