Catalogue of Digitized Medieval Manuscripts
http://manuscripts.cmrs.ucla.edu/
For sheer volume of manuscripts linked, the following site is unparalleled:
Large Digital Libraries of western manuscripts (constantly updated)
http://wiki.netbib.de/coma/DigitaleHandschriften
Below, I have included a block of links leading to collections containing fully digitized medieval manuscripts, 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.