In reply to James Gordon:
I use powerfull lights for night orienteering and have found that a miminum of 1000 lumins is essential. Go for Li-ion rechargable batteries, they are cheaper to run.
A lot of orienteers have bought head torches from www.brightbikelights.com. Their O set is very popular, it has a wide beam and you can adjust the brightness setting easily. It tends to swivel on its mounting a bit during running, I've added a bit of rubber to increase the friction. This torch uses a remote battery pack so you have to use a sac or bumbag to hold it. If you're out longer it has the advantage that you can use a second battery pack.
I now prefer their Ferei HL50 which is brighter, more narrower beam, is more stable on its mounting and has the batteries at the back of the head. This lasts me a good 2 hrs on full blast.
Another good supplier is www.torchdirect.co.uk. They have a huge selection of Li-ion torches, mostly hand held though. Fenix and Nitecore are really good units.
All these torches are make in China and have lasted well. Beware of getting cheap stuff from ebay, they seem to be unreliable, connections breaking and circuit boards blowing.