I grew up on a diet of Sci-Fi and stil think that Andre Norton's series Witch World was ground breaking in the blurring of lines between Science Fiction and Fantasy.
Anne McCaffrey is one of my favourites, both for the Dragons - a wonderfully constructed world and social system, and for straight Sci-Fi.
I have read the Thomas Covenant books, and various of the David Eddings sagas, and enjoyed them, but am not well up on the other current crop of Fantasy saga writers.
Another favourite writer of blurred fantasy is Clive Barker, who although he started writing straight Horror, moved with Weaveworld into a universe of fantastic beauty and grotesques. I find his writing style compelling, although sometimes it slides into the realm of the unpleasant.
J.G.Ballard - more fantastic and grotesque worlds, which although sold as science fiction, never really fitted with the rest of it. Then after I read Empire of the Sun, based around his experiences as a boy prisoner in Japanese prison camps during the second world war, his writing style suddenly took on a completely diferent perspective.
Just a few random thoughts on the topic.
Quack!
GtD!