Internet Jewish History Sourcebook
Although dedicated to providing a comprehensive historical survey of Jewish culture, this site also includes a section solely on Judaism in the Middle Ages (under Jewish Middle Ages). This section includes both general information as well as more detailed notes and primary sources on Medieval Jewish culture. For instance, one link presents notes and documents related to the affect of the Black Death on the Jewish population. The site is very well organized, easy to navigate, and should prove useful to any users pursuing this area of study.
ORB: Medieval Jews and Judaism
A section of the On-line Reference Book for Medieval Studies, this page offers essays, primary sources, bibliographies, and other online resources related to Jews and Judaism in the Middle Ages.