This Men at Arms book here I liked. I don't know much about the period but the artwork by Angus McBride was very evocative. Here are a few of the best.
The Arthurian Age; the Celtic Twilight; the Dark Ages; the Birth of England; these are the powerfully romantic names often given to one of the most confused yet vital periods in British history. It is an era upon which rival Celtic and English nationalisms frequently fought. It was also a period of settlement, and of the sword. This absorbing volume by David Nicolle transports us to an England shrouded in mystery and beset by savage conflict, a land which played host to one of the most enduring figures of our history – Arthur.