The Sword of the Rightful King, by Jane Yolen, found at the library category
I really like Jane Yolen and I love the Arthur stories, so this one seemed like a safe bet. However, I wasn't crazy about her Young Merlin trilogy. This one, happily, wasn't really connected with the Merlin stories. It revolved around Arthur, Merlin, Gawain and Morgause and a newcomer to court, the confusingly named Gawin.
Morgause is her normal rotten self, Gawain was a hero as always (he's my favorite, really), and there was much intrigue. I wound up only giving it 3.5 stars though, because the plot was just too complex to be believable. Arthur here was very easy to like. If you enjoy the Arthur stories, I think this one would be a fun one.