I'm trying to warm up to rechargeables but the lithium primary is still my go-to for emergency gear. One of my favorite headlamps nowadays is the Fenix HM23. It uses a single AA (any chemistry), has just 3 levels including a truly useful LOW setting and has a hard switch. I really love this lamp! When camping I use a lithium battery but for nightly walks I keep an Eneloop in it.

But I have to admit I still use a lot of Petzl and Black Diamond lamps. I've got a Petzl CORE rechargeable battery cell that fits any of their AAA lamps and charges with a micro-USB. Against my normal biases and predilections I find myself using it a lot. Nice for my nightly walk, and when the battery dies it just goes on the charger instead of me trying to remember where I left the spares!