Here's a little something I put together recently, A Dark Eldar Quad Gun.
My biggest complaint about most Dark Eldar Quad Gun conversions I've seen is that either they are way to over the top or they clearly look like a slap dash gluing of random parts. I wanted mine to be functional, make sense and clearly have the Dark Eldar aesthetic.
It's made from a Eldar Support Weapon chassis, a Dark Eldar Ravager sponson and some sliced and diced Dark Lances, Heat Lances and Disintegrators. Some Raider trophy spikes and Talos sensor spikes were added to complete the DE feel.