LED is definately the way to go. bright enough to see without being overly blinding. Plus they use lots less power and produce lot's less heat.
I went with Super Bright LEDS and got these
ALM-B 6 and simply glued them in place using Seal All Glue. I cleaned the place I was going to glue with brake/parts cleaner let it dry then applied some of the Seal All to the location I was going to put the light and then directly onto the back of the light. Waited about a minute for the glue to begin to set, then placed the light into place with a little bit of push to ensure a good seal then let go after about 30 seconds. No drilling no muss no fuss.
I did recently have to re-glue a light into place after a season of wheeling. But it seemed as though I was being a little frugal with the glue and this was one of the first lights I glued into place. I reinstalled it and back to good to go.