Although every book should be more widely read than it is, the following five beauties have been particularly sorely neglected. These are favorites of mine -- the list, of course, could have been far, far longer.
Aquamarine by Carol Anshaw
This remarkable first novel traces three different possible futures, all stemming from a single cathartic moment in a woman's life. I found it stunning when I picked it up in 1992; I've still never read anything quite like it.
I Remember by Joe Brainard
This is one of the more peculiar books I've ever read, and I think about it often. Brainard simply accumulates anecdotal memories, one on top of another, deadpan, until they begin to add up to a life, and then to imply, mysteriously, the existence of a soul.
Atlantis: Three Tales by Samuel Delany
If Samuel Delany were writing in the same innovative, intelligent way and his books were not science fiction, he'd be known to every serious reader and not just a relatively small band of us.
The Mirror by Lynn Freed
Freed is certainly well-known enough, but I would like to move to a parallel dimension in which everything is exactly as it is in this dimension, with one exception: Lynn Freed is a huge bestseller, and "The Mirror" was among the most discussed books of 1998.
The Force of Gravity by Robert S. Jones
This brilliant novel, Jones' first, about a man's mental disintegration, was too dark and harrowing for just about everybody and didn't sell despite its strong reviews. It's a pitch-black gem, a terrifying book with the power to harm.