Fingerboard Workbook Series by Diane Allen
These workbooks are designed to help not only beginning players, but any violinist learn the where the notes are (all of them in any position!) on the violin.
Intermediate Etude Books
Excellent etudes by Amy Barlowe
Amy Barlowe's etudes are thoughtfully composed, highlighting stylistic aspects from different time periods.
Simon Fischer Online
You can order Simon Fischer products straight from his website now, although for US citizens it will be cheaper to order the "Basics" and "Practice" from Amazon. Fischer's website has books and a DVD that can not be found on Amazon.
Yost System books for sale
These out-of-print books on violin playing are now in print by the family of Gaylord Yost.
Sheet Music Downloads
This is an amazing resource for out-of-print sheet music. It is a treasure trove of old scores. I have found several pieces from here for our Baroque concerts. The site is a bit hard to navigate, but just go digging.
Accompaniment Downloads for Violin Literature
I find this to be a wonderful resource. Having the accompaniment to practice with is such an essential for training intonation and rhythm.
Classical Connect provides independent musicians with a new venue for their performances. Hundreds of classical musicians have taken advantage of this opportunity, sharing their music with listeners across the world.
Old Time Jam
Large repository of backup tracks for fiddle tunes.
Other theory/note reading resources
Fingerboard Workbook Series
These workbooks are developed by Diane Allen, an expert contributor on Violin Lab. These workbooks are excellent for learning fingerboard geography.
String Class Fingerboard Geography- (An Intonation, Note-Reading, Theory & Shifting System)
I highly recommend getting this book.
Violin and Viola Lessons Connecting Note Reading with Note Placement
by Diane Allen who also wrote the Fingerboard Workbook Series
Suzuki Note Reading for Violin
by Sinichi Suzuki. This is great for people who know the Suzuki songs already.