Philadelphia native Lloyd Alexander's decision in the late 1950s to switch his literary efforts to children's books has resulted in some of the best young adult fantasies available. The Prydain Chronicles are classic fantasy, and I'm looking forward to giving copies to my neices and nephews.
Alexander is profiled by The Scoop, an internet magazine that covers children's book news. The Internet Speculative Fiction Database includes a bibliography. You can also find biographical and bibliographical information (and a recorded greeting from Lloyd Alexander himself!) at The Author Corner, a very nice site featuring the works of Mid-Atlantic States authors sponsored by the Carroll County Public Library of Westminster, Maryland.