What to read after Notes from the Underground?

Notes is considered by many to be one of the first existentialist novels. It presents itself as an excerpt from the rambling memoirs of a bitter, isolated, unnamed narrator who is a retired civil servant living in St. Petersburg. The first part of the story is told in monologue form, or the underground man's diary, and attacks emerging Western philosophy, especially Nikolay Chernyshevsky's What Is to Be Done? The second part of the book is called "Apropos of the Wet Snow" and describes certain events that appear to be destroying and sometimes renewing the underground man, who acts as a first person, unreliable narrator and anti-hero.