There are a million of them out there; Radio Schlock sells some that are cheap, and some that are better.
The two main issues are -
A) They should be gold-plated, to insure that they do not oxidize and produce dielectric effects, affecting signal quality, over time.
B) Some of the insulating materials can soften and physically distort the shape or spacing of the connector due to soldering heat. Teflon is of course the best for several reasons, but there are many less expensive plastics that hold up well. Try some before you buy in quantity, and see how well they withstand heat.
Another thing; use alcohol and a small acid brush to remove all traces of soldering flux from them when finished; it comes of easiest when still warm and soft.
A couple of layers of heat-shrink tubing is good for color-coding and stiffening the cable-connector junction to minimize flexing and wire fraying over time.