History.com: the Black Death - a great, well written and segmented site with heaps of videos and photos, very clear.
Eyewitness to History: The Black Death, 1348 - covers the The Signs of Impending Death, Varying Reactions to Disaster, The Breakdown of Social Order and Mass Burials.
The Science Museum: The Black Death - this is a fun interactive site where you choose right or wrong answers to questions about the Black Death
National Geographic: Plague - a short page with lots of facts about the Black Death
PBS Secrets of the Dead: Mystery of the Black Death - this is a very informative site including a description of the Black Death and has stories of the Plague
PBS Secrets of the Dead: Clues and Evidence - a medical view about the Black Death
Museum of London The Great Plague of 1665 - gives a pocket sized overview of the the plague outbreak, includes primary sources