I do most of my trailrunning in the Arizona mountains at night; and these runs tend to be about 2 hours each - so my setup is tailored to this context. In the desert, I don't have to worry about branches overhead, but the trail is extremely rocky and technical in many places, so I need very good depth perception or I trip over things, roll my foot, stub my toes, step on snakes, etc etc. The hills have eyes -- often many eyes -- so I like to have one powerful light which reveals my company
If you are running competitively, I would take ultrarunner's advice and stick with 3 AA lights - however, I don't run competitively so I choose differently. I run pretty frequently, so I use rechargeables. I personally find AA Sanyo 2700 mah NiMH (or Eneloop) and AW 18650 the best rechargeable options.
Like UltraRunner, I also recommend three lights, but I use all three at the same time (more below). I find looking at 3 (even 2) concentrated beams very distracting and uncomfortable. I choose two very floody beams and one thowy beam; this seems to be less distracting for me.
First, the headlamp. I tried the Myo-XP (pre-2008 and 2008), 80 lumen Princeton Tec Apex Pro, Primus PrimeLite Race. I settled on the Primus, however, now I use a Fenix LD20 in a Fenix headstrap which is slightly modified. This gives me 180 regulated lumens @ 2 hours on 2 NiMH. The LD20 has a great beam.
The Fenix headstrap comes with two flashlight holders and one battery holder; I took the battery holder and cut off the cylinders so that it is a flat piece of plastic. It is made out of PVC which is gummy, so it doesn't shatter / crack easily. This let me use the top strap which I find helpful in stabilizing things. So on one side I had the LD20, and the other side just the smooth and flat plastic 'plate' which attaches the top strap to the headband. If you go this route, make sure you slide the LD20 as far back as it can to minimize messing up your peripheral vision. I tried other lights but they hurt my peripheral vision due to reflections from the bezel or whatever. The LD20 is relatively light (56g w/o batteries), so it won't bob much. The new EagleTack P100A2 may be interesting, but its much heavier.
I tried using two lights on the headsteap, but its quite busy / awkward / heavy / silly looking (not that the wildlife cares).
Second, the handheld torch. For some reason, I really like being able to put light somewhere without turning my head (as required with most headlamp only setups). I wanted something very floody, because the light will naturally bob with your pace. If its a laser-skinny beam, it will be all over the place - a nice big flood kind of makes it somewhat less noticeable. I tried Fenix P3D, PD30, JetBeam Pro III ST, and Wolf Eyes Sniper MC-E. Currently, I use a Wolf Eyes Sniper MC-E. You will probably only need to run this on medium, it is insanely bright with wide & beautiful flood. If you hold it at waist height, you get a great view of the countours in front of you because the shadows accentuate things. I can't say enough good things about this torch. Relatively speaking, its also not very heavy. The only minus is that on medium / low, PWM may be noticeable when the light and you are moving - it doesn't bug me, and I'm usually sensitive to these things.
Third, waist light. This is optional, but I find it very useful on technical parts. I use a ZebraLight H60 mounted to the waist strap of a CamelBak Octane 8. It faces down at a 45' angle, and at this height gives a great floody beam showing the rocks and snakes within a few feet of me. If you don't use a pack with suitable belt, you can try a Patagonia Stretch Wading Belt, or a belt / fanny from Nathan / Ultimate Direction / Amphipod preferrably 1.5" wide, as the H60 w/18650 will cause narrower belts to twist and bob while running. To keep the H60 from moving, I used 2 wide rubber-bands that held my broccoli florets from the supermarket together
Put one rubber band over the knurling on the tail-cap for extra grip.
Buying all of this in one go is pretty expensive, I cobbled this setup together (if that isn' obvious) from lights I bought over time for completely different reasons - it just happens that the combination works very well for me.
I keep all this in/on my CamelBak Octane 8. It has two pockets on the waist belt which can take you spare batteries.
If you are racing, keeping all three lights going can be a bit over the top & distracting. I would recommend ULtraRunners setup: the headlamp and the handheld light + 1 backup. I have used just the Wolf Eyes at times, and for hands-free operation attach it to my shoulder strap (although I don't run with it like that). Also, another drawback is that I'm using 2 battery types, which is suboptimal in some ways.
BTW, my dog runs with me often and wears a ZebraLight H30 on top of his head
I think we probably look like a UFO sometimes.
