I posted this some time ago at CPF. I've got one of the same types of headlamps as danton and I found that it easily takes a P60 dropin.
I recently upgraded using the XM-L three-mode dropin from Manafont. It rocks. I also chopped off the battery pack and built an 18650 holder out of black PVC and a road bike tube. I wrapped the dropin in aluminum foil and found that it transfers heat pretty well. I will probably get some of the decent copper foil off eBay later on.
Here you can see the weight in oz with batteries and without:
A size comparison shot with the rechargeable AAAs I use.
A size comparison with my Surefire 6P:
The battery case is cheap, but not too flimsy. It comes with a large o-ring, but I wouldn't want to dunk it under water. It will probably shed rain just fine, but I never tested it since I replaced it with the 18650 holder. One very nice feature of the case is that the lid, which snaps on, is attached by a metal ring, so you don't worry about losing it or holding it while changing batteries. Very nice. The battery contacts are cheap and one popped out while pulling out a battery. A dab of glue will fix it.
The base of the light contains a simple clicky switch setup with a spring that provides a contact to the emitter. There is a metal contact that covers the spring, which popped off the first time I took it apart.
Here you can see all the components, my only concern is the multiple paths required for heat to leave the body. All the connections involve threads, so I ended up smearing thermal grease to help heat transfer between each component.
The reflector is low quality smooth plastic. The lens on this light is really poor quality glass and has a few marks out of the box. The body is in fact aluminum, only the reflector and the adjustable base are plastic.
The light does protrude a little from the head, but it is so light you don't even feel it. Since it will be on my helmet I don't care, my visor will block it anyway.
And, of course, I must have beamshots. My old camera didn't take the best shots, but here are some using the stock emitter. On the left is my 6P with a R2 emitter running off two RCR123As, on the right is the 3AAA headlamp.
The R2 is a good bit brighter, but also runs with more juice. The picture below is the same shot, but with an adjusted exposure.
For $14 I didn't expect much, but I like the headlamp and think it is well worth the money. The fact that I can upgrade it easily makes it a steal.
I used this light all last summer for early morning commutes and late night rides. I have used it on and off road and love it. I used an R2 dropin from DX until the XM-L came out from Manafont. Having three modes is wonderful. I will probably be ordering at least one more from one of the variety of sites that offer it. Now that I have the XM-L I can't wait to ride around at night. I will try and get a picture up of the new battery holder when I get a chance.
You can get it off eBay or from a variety of sources. I paid an extra $3 because I didn't like the woodgrain.