I have the Sidetrak (works well with linear brakes) and the Space Bar (works well with cantilevers). I have modified each with 1" aluminum tubing so that my light mounts fit better. The Space Bar is a little lighter but the Sidetrak can't slip on the bar.
I am particularly drawn to the Nitto Lamp Holder, but have never actually purchased one. They seem very nice, but they're also much more expensive that the roughly $10-$15 you might pay for a T-shaped Spacebar or the like.
I was looking at these too - but while I was in my basement (wood shop) I got the idea of building my own. So I took some nice Walnut, cut out some pieces, drill some holes, made a dowel and then finished it. I just got it put onto my bike last night. I should have measured some angles, since it needs a couple of degrees to counter the angle of the handlebar. I'll try to post a picture later tonight here and then another one in the commuter forum.