Oh, what wonderful taste you have! :-)

You need Peter S. Beagle's The Last Unicorn and his harder to find, Folk of the Air.

All of Diana Wynne Jones is good. The Dalemark Quartet.

I just finished Garth Nix's The Abhorsen Trilogy. I found it "difficult" kind of like the actual book, The Dark is Rising, the books were a bit scary for me, disaster looming on every page, kind of intense I guess.

You absolutely must read A Red Heart of Memories by Nina Kiriki Hoffman and then perhaps her The Silent Strength of Stones

I was surprised I didn't see any of Patricia McKillip. Start with the Riddle Master trilogy.

Tamora Pierce is very good too. The Circle Opens, Song of the Lioness, and Protector of the Small series and her new series Beka Cooper.

Madeleine L'Engle, The Wrinkle in Time quintet

The Pellinor Series (starts with The Naming) by Alison Croggon.

The Seer and the Sword and The Healer's Keep by Victoria Hanley. I handn't realized it was a trilogy; I just ordered the third in the series after I refreshed my memory about these first two :-)