Today's pick is a resource that will no doubt be of interest to pianists and other musicians. It is the Sibley Music Library of the Eastman School of Music.
The Sibley Library makes available for online access a great many music scores and music-related publications that are in the public domain. They have a notification service you can sign-up for in order to receive news of recent additions. Perpare to spend quite a bit of time at the computer screen as it's a large and interesting collection.
Check it out here.