I EDC an ARC LED light on my keychain, but its light is pretty minimal - better than none in the dark.

I like the single CR123A Fenix LED lights. Very bright for fairly small.

BUT ... these days I pretty much only use Princeton Tec EOS Rebel headlamps. I have them all over the house, in packs, in my car ... They use 3 AAA batteries, can use lithium batteries (some other headlamps can't), opens with a thumb screw (no prying or snaping - the plastic band adjusting loop can function like screwdriver on the thumb screw head if overtightened), provides an excellent combination of flood and stunning brightness for its size. They carry in hand as easy as on head. Wraps smallish - a 2"x3-1/4"x1-3/4" ball. Water resistant to 1 meter. About $30-35.

I find the lowest brightness (50 hours regulated) perfect for in-tent use, the medium (10 hours regulated) great for most uses, and the high (1 hour regulated) very bright. Actual total burn time is MUCH higher (121 hours at high). The blinking mode runs 12 hours regulated.

It has a tactile rubber button on top - easy to find. One click turns it on in high. Two rapid clicks in medium, three in low, four in blinking. Wait a few seconds then click to off. Simple.

Oh, and the EOS doesn't bother my glasses. Some semi-transparent headlamp cases inject terrible glare into my glasses.

Sorry for the length, but I like the PT EOSR that much.

Ken