Probably Dumas' The Count of Monte Cristo for me. It's one of those rare works that truly has everything. When I was in China 5 years ago I read it three times in three weeks, despite it being 1400 pages long. I don't think I can give a stronger recommendation than that.
I'm also quite partial to the short fiction of Akutagawa Ryunosuke. I particularly enjoy his early, myth and folklore-inspired tales and the autobiographical descents into madness he composed shortly before his suicide (the historical pieces he wrote in the middle of his career never impressed me as much).