Shadow Wars Trilogy by George Lucas and Chris Claremont - This is supposed to be based on the movie Willow, but even if you've never seen the movie this is a great, great fantasy series. I wish there were more than three books, but obviously both authors are famous and too busy to work together on such a time consuming project as a novel again. I'm just happy that these three novels exist.
It's one of those series you forget you own then find gret delight in finding and rereading them over and over again.

The Charioteer or really anything by Mary Renault. She writes historical fiction with occasional homosexual themes but don't get put off by this (no sex is graphically written, everything is very subtle or implied considering it was written in 50's-70's) She wrote an excellent trilogy on Alexander, as well as other Greek historical fiction novels. They're very accurate and well researched.

Ender's Game by Orson Scott Card - I'm not a huge fan of any of his other books, but this particular one is fantastic. I would recommend it whether you're a sci-fi fan or not.

Summers at Castle Auburn , Samaria Series, Thirteen Houses Series by Sharon Shinn. She also wrote some fun young adult books. Summers at Castle Auburn is pure fluff fantasy one-shot. Just enough fantasy to keep it this this side of Fantasy versus Romance but if you just want a quick heart-warming story I highly recommend this.
Samaria series is about winged people who pray and watch over the people of their country. If you're fascinated by angels, this is a very good series, though it gets more into sci-fi as you go on. Like most of her books, the stories usually revolve around one main couple that you van't help falling in love with.
I'm not as far into the Thirteen House series, but it's the most generic fantasy of her series. However her writing is easy to read, and her stories flow nicely. My only complaint is since every book is from a different character's view, you miss the original characters being more involved.

Firekeeper Series by Jane Lindskold If you like the girl raised by talking wolves kind of stories like I do, at least the first three books are very good, with those thereafter tapering off a bit.
She also wrote Brother to Dargons, Companion to Owls which was excellent, about a girl who can't speak except by quoting from books she's been read. It has a fantasy side too, she's really not just crazy though that would have also been a fascinating story.

It was already mentioned, but I also highly recommend Robin McKinley's work. My favorites are Sunshine, Deerskin, and Beauty.

I may think of others later...