International Music Score Library Project (IMSLP)
A virtual library created, based on the wiki principle, to gather public domain music scores as well as music scores of contemporary composers who wish to grant free access to their works. IMSLP provides access to a large array of public domain music scores. Over 6,500 composers are represented, and multiple editions, arrangements, and parts are available for some works. For most scores, the publication information is noted; however, some scores do not indicate the publisher and some have been re-set in programs like Finale or Sibelius. For public domain music editions, check here first.