Bodleian Library Broadside Ballads
"The Bodleian Library in Oxford has unparalleled holdings of over 30,000 ballads in several major collections. The original printed materials range from the 16th to the 20th Century. The Broadside Ballads project makes digitised copies of the sheets and ballads available to the research community"
...and of course to singers looking for printed sources of songs and ballads which passed into the oral tradition (Oxford City, for example) as well as those (The Oxford Ramble, to name but one) which didn't!