Set in the present day,
Holes by Louis Sachar has what may be the most intricate plot I have ever encountered in any medium. It also has a dark sense of humor. And it's technically a children's book.
As for epic fantasy adventure, it's hard to beat
Ursula K. Le Guin's A Wizard of Earthsea. It's got four sequels, but none of them recapture the appeal of the original story. The first, though, is most definitely worth your time.