http://imslp.org/wiki/ International Music Score Library Project
`The International Music Score Library Project (IMSLP) is a project for the creation of a virtual library of public domain music scores, based on the wiki principle. Since its launch on February 16, 2006, more than 20,000 scores, for 11,000 works, by over 1,200 composers have been uploaded, making it one of the largest public domain music score collections on the web.