Catalogue of Digitized Medieval Manuscripts
http://manuscripts.cmrs.ucla.edu/
Below, I have included a block of links leading to collections containing fully digitized medieval manuscripts (over 13,000), one for digitized individual manuscripts, and one devoted to projects choosing to digitize selected pages for things like illustrations, examples musical notation, etc. This page is part of the Andy Holt Virtual Library's section on medieval source-based textual scholarship. You may also wish to consult some of the incunabula readable on line.
I call your attention to the latest Andy Holt Virtual Library project involving links to medieval manuscript facsimiles:
Manuscripts of Medieval France with Vernacular Texts
http://www.utm.edu/staff/bobp/vlibrary/frmedmss.shtml