This Korg metronome costs from $15 to $20 and is available from most of the businesses listed on the "Links" page, in addition to Amazon.
Made by Qwik Time, this is a very thin metronome and easy to fit in a violin case. It is available for about $10.
This is a Korg chromatic tuner, helpful for those who are still developing their sense of pitch. It costs around $20.
A basic pitchpipe is also a good tuning aid. You can pick one up for about $3.
Music Stands
Hand Strengthener
Everyone needs a music stand! If possible, get something sturdy like a Manhasset - a solid music stand makes it easy to add pencil markings to your music. This model, available in about 10 colors, runs about 42-45 dollars. They also carry a "Voyager" model, which has a collapsible base and is good for travel ( about $10 more than the basic model).
Another option are these cute and colorful folding stands, made by Gig-N-Go. They cost around $27.
These are made by Gripmaster and are about $13. They are good for strengthening weak hand muscles. I use one of these when I am on an extended (sans violin) vacation to keep my strength up!
Other supplies
Other supplies you will need are rosin, a soft cloth to clean your violin, peg compound for those sticky pegs, and perhaps a humidifier for your case.