Over the last few months the Katzen Music Library has been scanning their public-domain historical sheet music and adding it to an online collection system. The full digitized versions are available to browse, print, and save. You can check out the online collection page to see what's available.
They currently have more than 100 items uploaded, but this is still very much a work in progress. If you have any feedback, be sure to let them know either in person or in the comments section of the Katzen Music library blog post HERE.