Here's a book I've seen sold in a few places, and reasonable at $8.00.
and here are links to two sites with midi files of medieval music
I hope you find something that appeals to you!
I'm a newbie both to this site and to the BP (just got a Tenor and Tenor D from Rick Long today). The following are some links I have to early and not so early recorder music:
These sites are a mixed bag of written and/or audio (usually midi) files. A lot of them are full scale works but there are some gems of tunes to be found as well.
Try this link - it's a great resource for Renaissance/Medieval tunes. Perhaps more Renaissance than Midieval but the dance tunes are great!
I like one called Renaissance Festival Favorites. I also recently got one called The Renaissance Fiddler. I don't know how psaltery-friendly the tunes are; I play them on fiddle. Some are pretty notey, but not all.
Cantiga has sheet music on most of their Renaissance stuff.