You might have noticed mine - I have a SpaceGrip type thing (random brand, picked up at York rally) on the little stub on the mech post, so that I can mount two lights on it, rather than one on the stub. At the moment it's just two Smart 5 or 7 LED front lights - eventually I'll upgrade one to a Hope or something.
I fitted another SpaceGrip type thing to the rear triangle frame of the Dash - the frame tube is quite a wide bore, and most light brackets wouldn't fit. I have another SGtt spare, which I intend to mount on the other side to carry another rear LED - on that Scarborough ride I just used a velcro strap to attach the light on the nearside.
I also have a pair of Skullies:
Skully Ultra Bright Mirco LED Bike Light £7.50 | which fit to any size of tube with rubber straps. The rear one went on the rear triangle, low down, and the front one around the very bottom of the front mech post - it pointed upwards a bit due to the angle of the post, but actually, it dud a very nice job of illuminating the BB and cranks, creating a rather comforting pool of light between my feet.
By the way, thinking of my side by side lights, a friend told me about a mate of his who used to like to ride his motorbike between cyclists riding 2 abreast, to scare them. One night (and don't ask why he didn't have a headlamp on or see in time, I dunno), he discovered that the two faint little red lights he was rapiding catching up with were in fact on a rather elderly Bedford van.