Here is a site where you can download 1,595 pieces of classical sheet music for free. The site is called the Mutopia Project. The sheet music is free to perform, print, modify and distribute. These are editions that are already in the public domain.
Composers include Bach, Beethoven, Chopin, Handel, Mozart and more. There are even a few modern day composers such as John Phillip Sousa. There is music available for Piano, Voice, Organ, Violin, Guitar, Orchestra and more. You can sort by instrument, composer or style of music.
Visit the Mutopia Project and download free sheet music.