The Gormenghast Trilogy (Titus Groan, Gormenghast, Titus Alone) - Mervyn Peake
(put on my reading list at somebody's suggestion, but I haven't been able to remember whose)
A vast yet isolated fantastic world peopled with eccentric characters, I'm surprised I had never heard of this before college and that so few people I've spoken to seem to know what it is. It's been compared to Tolkien, but it's not quite the same: the writing is almost flowery at times, and Peake can spend an entire page describing someone's profile, or at other times cover a week's travel in a paragraph. The first two books were made into a miniseries by BBC but I've yet to see it. Also of note: the books were highly regarded by C.S. Lewis. How can you go wrong?
Now that I've finished the trilogy, I feel I should say more. I liked the first two better than the last, but this doesn't mean the third isn't worth reading. This is one I'd recommend to anyone who's a fan of the fantastic or mythical, and is prepared to immerse themselves in a different world for a good long soak. From Anthony Burgess' introduction to the books:
It remains essentially a work of the closed imagination, in which a world parallel to our own is presented in almost paranoiac denseness of detail. But the madness is illusory, and control never falters. It is, if you like, a rich wine of fancy chilled by the intellect to just the right temperature. There is no really close relative to it in all our prose literature.