how about the Streamlight Twin Task on LED mode. I believe it's in direct drive. Obviously the incandescent lamp won't work, but the LEDs run pretty well on low battery.
The TT-1 uses a step up circuit which doesn't provide as much light as the X5T with old cells. The 2-L may be better but I haven't made the comparison.
another vote for the Inova X5T, check out the HA3 version sold by www.countycomm.com if they still have it in stock (it's a great deal on a great light) /ubbthreads/images/graemlins/smile.gif
Check out Tek-tite's Splashlite Led too, runs 1x123 cell, and much like the X5t as well in terms of sucking those batteries dry. I still get some light out of 123s that will no power my KL1/E1e and Arc LSL.