The Middle Ages are a fascinating epoch. You will find plenty of information within the following articles.
Medieval History - The full history of the Middle Ages with plenty of links. This is a quasi-complete stop for one's medieval studies. It takes the reader from the year 476 to the fall of Constantinople with an in-depth study of everything in between.
Medieval Glossary - Contains the definition of the most important and common medieval terms that are required to know in order to understand medieval history.