This site has a range of manuscript resources, information, and links that covers British manuscripts from roughly 1000-1500.
Manuscripts of the West Midlands
This catalogue of vernacular manuscript books of the English West Midlands, c. 1300-1475, includes images and information about individual manuscripts including contents and provenance.
A Digital Index of Middle English Verse
This is the single most useful too for a student of medieval poetry. It includes indices organized by poem, by manuscript, by location, and more.
medievalbooksandmore 