I usually stay on the English Wikipedia, though I occasionally come here to upload a new or higher-resolution manuscript image. Here are my favorite contributions:
The first page[1] of the 1st edition of Edmund Spenser's The Faerie Queene
The first page[2] of the MS of Sir Gawain and the Green Knight
The page of the MS of Sir Gawain and the Green Knight featuring the illustration[3] of Gawain chopping the head off the Green Knight
A MS illustration[4] of Marcion of Sinope with the apostle John