You don't say whether you're after retellings of the Arthurian myths or original fiction based on them, but some others I can think of are: The Mordred Cycle by Haydn Middleton (comprising The King's Evil, The Queen's Captive and The Knight's Vengeance), which retell the story from Mordred's viewpoint; Nancy McKenzie's The Child Queen and The High Queen (recently reissued in an omnibus as Queen of Camelot), which are about Guinevere; Alice Borchardt's The Dragon Queen, which is an original story about Guinevere; The Enchantresses by Vera Chapman, which is about Morgan Le Fay; and, of course, T.H. White's The Once and Future King, which is generally regarded as one of the best Arthurian fantasies. Stretching the definition a bit, Gwyneth Jones has recently begun a near-future sequence with underlying Arthurian themes; the two books published so far are called Bold as Love and Castles Made of Sand. And there are plenty more than just these: if your local library has a copy of John Clute's and John Grant's Encyclopedia of Fantasy, check out the entry on Arthur for a good general survey.