Tools to slow down your music during practice you will find in the "Software and Apps" section
Websites for Piano Accompaniments
Piano Accompaniments for Violin Solos
I love this website. The owner Paul Gardner has made accompaniments to much of the standard student repertoire for violin. The list is quite extensive and his playing is wonderful. Not midi!!
A Collection of Accompaniments for Various Violin Solos (for download)
Accompany - Wonderful Piano Accompaniments Website
This is an amazing service. All of my private students are now subscribers. Runs on Windows, Mac, and mobile devices. It features many student pieces, scales, drones, etudes, as well as concertos, sonatas, etc.
Youtube channel with piano accompaniments.
Accompany - Suzuki Version
Steven Maloney now has accompaniments for all the Suzuki pieces. Like on the general Accompany site you can slow down the accompaniment or loop sections.
Large Library of Violin and Orchestral Accompaniments for Purchase
Repertoire (various)
This company makes books and practice CDs for scales and violin literature. The Cds feature slower practice tempos and real orchestral back up tracks.
Accompaniments for Suzuki Songs
Suzuki Repertoire Downloads (and others...)
Accompaniments to Suzuki Songs
Suzuki Violin School, Vol 5: General MIDI Disk CD-ROM
Most other Suzuki volumes are also available with an accompanying CD.
Alan Chan's YouTube channel
Fiddle Tunes
Old Time Jam
Large repository of backup tracks for fiddle tunes.
Christmas Carols - Audio
Sheet music for Christmas Carols
In the "Sheet Music" section you will find the PDF files for these songs (under "Christmas Carols").
Accompaniment for Scales
One Octave Scale Piano Tracks
A collection of one-octave scales in various tempi to use for practice.
Website with drones for scale practice!