I just went through this myself and ended up with the Black Diamond Moonlight.
This is going to sound like an advertismesnt ripped off some webpage, it's my own words though.
The Moonlight's electronics are redesigned for 2003. Instead of playing the game Petzl did and adding another model they just give you more for the same price. The old Moonlight switched on and off. The new Moonlight switches on and has 3 brightness modes + blink. I recently used it on a scout camp and found it to be a fantastic light. The batteries go in a compartment on the back of the headlight (IE that rests at the back of your head) and then a thick cable carries power to the electronics and LEDs at the front of your head. To switch on you press a small button on the bottom of the headlamp. It is a reverse clickie--ie once you have it on pressing the switch half way causes it to turn off. This is how you change modes, by turning the light off and back on quickly. It sonuds odd but I actually really like it. From off the light always starts in 'on' and then you just quickly activate the switch half way for dim or dimmest. The nice thing about this is it's easy to switch back to the brightess setting, you just hold the button half way down for about 3 seconds and when you let go the light thinks it has been switched completely off and back on so it comes on at full brightness. The only bad thing I guess is that if you turn the light all the way off and then, for some reason, need it back on within 2-3 seconds it will come back on but at a dimmer setting. The LEDs are dimmed by using PWM so you get a fun ultra-fast strobe effect when they are dimmed. I don't know how battery life is but I got a week of playing with the light at home plus a week of using it several hours a night in and am still using the same set of batteries.
The light easily ajusts up and down which I found nice (Ajust down to the perfect angle to eat in the dark, up to walk on paths, etc.). Because the batteries are on the back of your head there is little weight on your forehead and the light itself doesn't bounce around a lot.
On the camp I had my Arc AAA, McLux, Energizer Folding LED light, $2 Radio Shack Flouressent light, Brinkmann Legend LX and my Surefire G2Z--the Moonlight was used for 99% of my lighting. Even if I needed a light in the middle of the night to check the zipper on my sleeping bag or something it was easier to grab the moonlight and switch it on than to pull my Arc out of my pocket and twist it on.
For $30 I feel the light is a steal. I was actually able to get mine for $20 on sale at the Black Diamond store. Black Diamond is a local, employee owned company thats in it for the love of sport--not for money, and it shows in their products which they stand behind 100%
PS--It's 4 LEDs and I forgot until after I posted, but currently (As of July 22 2003) my avitar pic is actually a pic of me wearing the moonlight.
PPS--Larger version of that pic