The Art of the Bow: "A revolutionary DVD combining the highest levels of music pedagogy and performance, digital video, and bio-mechanic motion capture technology." Created by Hans Sturm and based on François Rabbath's bow technique.
Robertson and Sons Violin Shop: Shop located in Albuquerque, New Mexico. Expert repair, bow rehairs, and an excellent instrument/bow selection.
Quantum Bass Center: Shop located in Houston, Texas. They not only have a selection of instruments, bows, accessories, Laborie-style endpins, and sheet music (including my own printed editions), but they also regularly offer classes and workshops.
Bassrosin.com: I like to replace the Pops I use in orchestra fairly often, here is where you can get the latest batch.
Ovation Press: Edited orchestral parts by Paul Ellison, Ed Barker, Lawrence Hurst, etc.
International Society of Bassists: Membership provides access to a wealth of bass information--definitely worth being a part of.
Cluster Research, Bass Wheels: Great bass wheel. I bought mine in 1990, put a lot of miles on it, and it's still going strong.
McMaster-Carr: Source for rubber bow tubing. Look for 1/2" ID, 3/4" OD, 1/8" Wall as a starting point.