I believe he would have added 'The Black Company' by Glenn Cook, based on the glowing review he made in one of the old Dragon magazines.
'Old Nathan' by David Drake is a collection of short stories set in the Appalachian Mts. about a cunning man. I enjoyed the book.
Rather than Wellman's 'Beasts from Beyond' which seems to be hard to find, judging by the price, I might substitute almost any of the Silver John stories.. there are many, all excellent.
Lin Carter edited the Ballantine Adult Fantasy series during the 70's.. it had some of the books on Gary's list as well as other, lesser known books. Some I found to be rather slow (Eddings), but others have been wonderful. The collections of Clark Ashton Smith, 2 collections of short novels and Mirrlees' 'Lud in the Mist' come to mind.
C. L. Moore's stories of Jirel of Joiry seemed to have escaped this list.
Although they may seem out of genre, I'd suggest M. R. James to any fantasy or horror fan.
For more modern books:
The Drawing of the Dark.. I believe it's by Pratchett.
Neil Gaiman's fantasies, as well as those by Mievelle.
I haven't read a book by Jim Butcher that I didn't enjoy.
'Scar Night' by Alan Campbell
'Jonathan Strange and Mr. Norris' by Clarke ( my books are still packed up, I may be mistaken)
'Villains by Necessity' by Eve Forward
Stephen Brust
Tim Powers
'War of the Flowers' by Tad Williams (I realize he's written much more, but this is self contained)
Some of my later list is skewed towards steampunk, but I like urban fantasy as much as I do Sword and Sorcery.
That reminds me.. Hawk and Fisher, by Simon Green
I hope my additions will be of some use to you, even though many of the later books may be fairly obvious.
Jon