This is a true classic of dark fantasy/horror.
Robert Neville is the last man on earth. He finds himself surrounded and accosted by vampires created by a highly contagious bacteria. By day, he hunts and kills the monsters. By night, he boards himself into his house to wait for the rising sun.
Although his existence is frustrating, he survives quite well until a group of "still-living" vampires finds a way to halt the bacteria, and form a new society.
Although this book loses some of its original power, being set in the "distant future" of 1976, it's still a very moving and haunting book. It's dark and gritty, but at the same time, there's a wry humor about the whole situation.
While vampire novels have become a dime a dozen lately, I can't think of very many that compare with this one. It's one that has stood the test of time, and will continue to do so.