The Winchester Troper is an 11th-12th century manuscript containing some of the earliest music in England. There's a new facsimile edition out. The $220 price tag is rather steep, but it's also at the UMD Performing Arts Library (in the Reference section, alas, so no checking it out). The same scholars have put their learning into practice, with a CD of music from the Troper also available. At $47, the CD ain't cheap, either, but I may just have to pick it up.