I'll second Bleak House. I just got a big Dickens anthology and have been meaning to go it, and HarryT (who reads a lot of classics) says Bleak House is Dickens best.
I also nominate 'Midnight's Children' by Salmon Rushdie. It's massive, and it's historical fiction, which I don't often choose. But it looks really interesting. From Amazon:
Born at the stroke of midnight at the exact moment of India's independence, Saleem Sinai is a special child. However, this coincidence of birth has consequences he is not prepared for: telepathic powers connect him with 1,000 other midnight's children all of whom are endowed with unusual gifts. Inextricably linked to his nation, Saleem's story is a whirlwind of disasters and triumphs that mirrors the course of modern India at its most impossible and glorious.