Lights that I am aware of that can accept a bulb more suited to the voltage of 4 NiMH AAs (a KPR103 bulb) are:
4AA Responder - my choice for this use
PT Tec40 -case pressure can deform NiMHs (mine did)
RayOvac Prodigy -about $6 @ Target
RayOvac 4AA Camper -weak switch, $4 @ Walmart
The Responder has a flood to spot focus, plus springs in the bottom of the battery well so the pressure on the batteries is less than the Tec40. Guys that run the Tec40 w/NiMH put tin foil in the bottom to maintain reliable contact. My Tec40 deformed the batteries so much, the light started to flicker on and off due to poor contact among the batteries.
You'll find lots of people that like the Tec40, for substituting PR bulbs though, I like the Responder.
If are willing to give up just a little brightness (not too much), I'd go with the UK 4AA AS2 (w/switch). I use this with NiMH and I REALLY like it! It is still plenty bright but really easy to pocket and the switch is great for one handed operation!
If pocket-ability is more important to you than maximum brightness (it was for me)...the UK 4AA AS2 is the one!