My favorites tend to be mostly fantasy or sci-fi (and I am trying not to name any of the obvious ones here: HP, LoTR, Narnia, etc):
Riddle-Master (trilogy) - Patricia A. McKillip - A gorgeous, epic, lyrical fantasy trilogy.... Love her spiritual concept of magic.
Winter Rose - Patricia A. McKillip - Dreamy poetic writing that transports you to the fairy world.
Dandelion Wine - Ray Bradbury - Described as a "love letter to his childhood" this is a semi-autobiographical tall tale about his childhood in the Midwest.
Godbody - Theodore Sturgeon - A non-genre gem by another sci-fi great. The story concerns a small town and a Christlike being called Godbody. And the particular glow of sunlight on tulips.
Ender's Game - Orson Scott Card - Hands-down one of the most gripping, engaging, touching, works of sci-fi I've ever read!
A Wrinkle in Time - Madeleine L'Engle - My husband and I met over liking this book. Seriously. It's just that awesome. "Wild nights are my glory!"
His Dark Materials (trilogy) - Philip Pullman - The books are infinitely better than that so-so first attempt at a movie. I especially loved the atmosphere and world Pullman created in these.
Galactic Milieu (trilogy) - Julian May - Wonderful, vibrant, characters and nicely imagined sci-fi setting. Humans with mind-powers. Check!
Otherland (quartet) - Tad Williams - Starts out in an alternate near-future South Africa and travels, through technology, into the realm of human imagination, mythology, etc... My kind of cyberpunk.
...And many more, but those will do for now