Hundreds of free (public domain), downloadable works. These are the composers' original works (not arrangements). Music includes solos, ensembles, and orchestral works.
http://www.8notes.com/instruments/
Solos, duets, trios, quartets, quintets, and string ensembles for printing. The works are organized by instrument and size of group, so music can be found quickly.
http://fiddlerman.com/studies-etudes-and-music/
Violin Only - Solos, etudes, and scales free to print
Create, print, and share sheet music online. You can find also find popular songs for strings that were arranged by other users.