I was having trouble finding a good wire clip, so I made one. This is mountable (size 6 screw), and once mounted, wires can be added/removed by simply unclipping the side. This is 3cm x 3cm, so it should hold a good number of wires.

If mounted on a vertical wall, the clip should be at the bottom (otherwise the weight of the wires will open the clip).

EDIT: I just uploaded a slightly better version -- it's a touch wider/stronger, and I updated the clip to catch a bit better.