Gina and I have run trails by headlamp and flashlight since we first got into trail running back in 2001. Due to time constraints, most of our fall and winter running occurs after dark. Both of us prefer to run on trails and don't want to let darkness keep us from staying in trail running shape. In addition, there are aspects of running at night that you just can't put into words.
My lighting preference is to use a LED headlamp and a flashlight (halogen or LED). LEDs are a very energy efficient lighting source and cast a white glow (I can't stand to buy and go through a lot of batteries. LEDs have really helped increase the run time of battery operated lights). Depending on your LED headlamp, the beam emitted will be a glow or a focused beam. There are countless options of headlamps for a variety of uses. I'm a fan of Princeton Tec lights. I've yet to find a headlamp that lights up the trail and allows you to get depth perception.
When running at night you get depth perception from shadows being cast from your light source. The best way to get shadows is to use a flashlight. Holding a light lower, in your hand, helps to get the shadows you need to identify rocks, roots, and other obstacles in your way. With this in mind I usually only run using a headlamp, but if I'm planning to run a trail fast, run a rocky orrooty trail, or run a steep downhill, I will also use a flashlight. Not only does this help minimize getting injured on the trail but it is also smart to have a backup light source in case your primary light stops working.
Three of our Sponsors carry flashlights and headlamps:
Dick's Sporting Goods