I've read a bit of sci-fi, but probably lean more towards fantasy division of sci-fi/fantasy
. I definitely go in cycles, and it's been a few years now since I was on a sci-fi/fantasy kick. These are some, in no particular order, that stick in my mind.
Tam Lin by Pamela Dean
Hounds of the Morrigan by Pat O'Shea
Douglas Adams' Hitchhiker books, and the Dirk Gently detective Agency books
War for the Oaks by Emma Bull
Neil Gaiman's works, particularly Anansi Boys and Good Omens (with Terry Pratchett)
Prachett's Disc World books, particularly the Tiffany Aching books
Golden Compass (Northern Lights) by Philip Pullman
Garth Nix's Sabriel, and sequels
Diana Wynne Jones books, particularly The Dark Lord of Derkholm
The Changeover by Margaret Mahy
Dealing With Dragons by Patricia Wrede
The Perilous Gard by Elizabeth Marie Pope
Tea With the Black Dragon by R.A. McAvoy
Jack of Kinrowan (Jack the Giant Killer/Drink Down the Moon) by Charles de Lint,
Susan Cooper's The Dark is Rising sequence
Anne McCaffery's the Harper Hall Trilogy and her Crystal Singer books
Winter of Enchantment by Victoria Walker
In a Blue Velvet Dress by Catherine Sefton
House on Mayferry Street (Flute in Mayferry Street) by Eileen Dunlop
The Snowstorm by Beryl Netherclift
And a few that stand apart as a bit more than fantasy, blending in theology or philosophy (or both)
The Space Trilogy (Out of the Silent Planet, Perelandra, That Hideous Strength) by C.S. Lewis
Diamond in the Window by Jane Langton
The Maze in the Heart of the Castle by Dorothy Gilman
Escape to Witch Mountain by Alexander Key
Whew, that's actually kind of a long list! I'm sure I've missed out a bunch that I've loved too....hmmm....feeling like I should pick one up now, but I can't, have Pony in the Luggage to read!