The Middle Ages from Annenberg Media:
http://learner.org/interactives/middleages/religion.html
Castles in Medieval Times
http://www.yourchildlearns.com/castle_history.htm
About.com: Medieval History
http://historymedren.about.com/cs/gettingstarted/a/welcome.htm
Medieval Weapons
http://www.pbs.org/wgbh/nova/lostempires/trebuchet/race.html
Medieval Times
http://educators.medievaltimes.com/#
Early Medieval Art
http://witcombe.sbc.edu/ARTHmedieval.html
Kidipede: Medieval Art
http://www.historyforkids.org/learn/medieval/art/
The Middle Ages from the History Channel
http://www.history.com/topics/middle-ages