I just though of another one; I'm not a fan of Arthurian fiction, primarily because the subject has been done to death and mostly not very interestingly, but Richard Monaco wrote The Grail Wars (late 70's and early 80's) and that was very well done imho. Apart from The Winter King etc. by Cornwell, these are probably the best on offer.
I loved Cornwell's Arthur books, but my all-time favorite Arthurian book was Marion Zimmer Bradley's Mists of Avalon. In fact, if I didn't have about nine gajillion other books to read right now, I would reread it because I've been longing to return to Avalon and Camelot.