From Melissa Kanell:

 http://www.youtube.com/embed/e-y581HdWfY?rel=0 

Notice the great bow hold and left hand relaxed and open for vibrato and shifting.  Also, see the parallel bow near the bridge and what a great tone results.

From Gabe Bolkosky:
Farm Animals and Twinkle Variation B
http://www.youtube.com/watch?v=mNH__Ybzfec&list=UUceznr2-0HxysJJOpgnrZgw&index=1&feature=plcp