Its pretty cool what you can do with two flash units these days. While shooting the restaurant for the upcoming Dining Guide I saw Josh doing his thing with fire at the bar.
I placed a remote flash unit to his left back and put a blue gel on it. The flash was aimed at the wall and his back. A second concentrated flash unit was shot off camera. I exposed for the background so the colors would show. Pretty simple really. If you don't have two flash units you can do similar things with flashlights and a sturdy tripod.