If the BandMusic PDF Library, offering free access to public domain band music, seems familiar, you might be thinking of the IMSLP/Petrucci Music Library, which does the same for classical scores.
Each of these should be on every library’s list of music resources.
Thanks to Michael Duffy for the link!
Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
Established July 2006
by Rick Mason