A very extensive site with links to many other sites. Not exclusively medieval.

"The CELT project is producing an online database of contemporary and historical topics from many areas, including literature and the other arts. It will provide material for the greatest possible range of readers, researchers, academic scholars, teachers, students, and the general public. The texts can be searched, read on-screen, downloaded for later use, or printed out."

The Christian Classics Ethereal Library (CCEL) seeks to build up the church by making classic Christian literature widely available and promoting its use for edification and study by interested Christians, seekers and scholars. The CCEL will accomplish this by selecting, collecting, distributing, and promoting valuable literature through the World Wide Web and other media.

Over two dozen collections of PDF documents of various texts from throughout the Middle Ages. Collections include an Arthurian Series, Medieval Catalan Series, Middle English Series, Medieval Latin and others.

"The Online Medieval and Classical Library (OMACL) is a collection of some of the most important literary works of Classical and Medieval civilization."

"Project Gutenberg is the first and largest single collection of free electronic books, or eBooks. Michael Hart, founder of Project Gutenberg, invented eBooks in 1971 and continues to inspire the creation of eBooks and related technologies today." Over 19,000 eBooks are available for download. Not exclusively medieval, but a lot of good stuff to check out.