Percussa micro super signal processor

Terry Smythe
has digitally scanned 2,650 vintage piano rolls (and counting) and
converted them into zipped-up MIDI file archives. Those are standard
MIDI files, folks, so fire up GarageBand or Live or whatever and see
what you can do with them!

Check out the technical details of how it was done; there are enough people doing this that there's even a Yahoo discussion group devoted to the topic. Then dig through the archive of piano rolls, free for non-commercial use, featuring vintage AMPICO, Duo-Art, Welte, and Recordo rolls.

Via the all-DIY Make:Blog.