I use a tens machine for stimulation, it has different pulse settings and adjustable intensity settings, some settings can be intense and sting a bit and others create a gentle throbbing feel.
I usually use square pads around the side of my cock head and set it to a gentle pulse and have managed to cum by turning the intensity up when my cock starts to twitch, I find it gives a mind blowing climax, for best results use a gel on the pads, or it can give a burning or intense stinging feel without.
The machine I use can have four pads operating at same time so can attach two to side of balls as well. Got a couple of pics on my page of the ones on my cock head. ;-)