The lyrics Monk sings to Dr. Kroger during their session to avoid conversing about his sex life is from the musical "Camelot" by Alan Jay Lerner which ran on Broadway from 1960 to 1963, and the song is titled "If Ever I Would Leave You".
Mr. Monk's words when wiping his hands with a dirty rag, "...Oh the humanity!", are exactly those spoken by the journalist Herbert Morrison when he was describing the crash of the Hindenburg.
Note the personal ad listed below the one Randy placed in the newspaper: "Benji, where have you gone? Desperate to reach you. Please call home. All our love, M & D." This is apparently an in-joke referring to Sharona's son Benjy.
The events of this episode are alluded to in the novel "Mr. Monk Is Miserable" by Lee Goldberg.