I'm a big fan of MCM electronics. Thing is they are not a retail operation as much as a manufacturing supply warehouse, so their catalog may seem rather cryptic.
I get all the parts for making my cables from them, and the prices are fantastic. I can make a 1ft pair of stereo interconnects (double shielded, teflon dielectric, and good looking and quality plugs) for $8, and then 14c/foot after that.
they also have pretty much any part you would want for making your own gear as well, like crossovers, amplifiers, etc.