I'm curious what people are using as well. I just purchased a small hat mounted LED device, clips to the bill of the hat with some metal clips. I'm still testing it out, but when I did a trail training run with a local group, I noticed that my hat light was drowned out in their much brighter belt mounted lights. Furthermore, it seemed to reduce my depth perception, making the ground seem much flatter than it actually was. A dangerous thing when you're running on trails. I think it'd be fine for level group and solo running easily enough though. Keeps the hands free.
I'm not sure I'd really like a belt mounted light though, on longer runs I'm usually wearing belt pouches for gels, salt caps, etc.