The flashlight is actually bigger than it strictly needs to be length wise but since I was using PVC as the body the dimensions were more or less fixed.
As said before, four Cree XR-e LEDs provide the illumination. They are attached to a heat sink that I pulled off a circuit board and ground down to fit inside the PVC housing. The FET came out of a stereo circuit board and the other transistor came out of a TV. I hunted down a few resisters with the appropriate values with my multi-tester and used those. I used a breadboard to build the circuit and test it using a 6v 1a wall wart that I had laying around and then later with the 4 Ds held in my hands with jumper wires on the terminals.
I did have to buy the switch. I didn't have anything but a bunch of really ugly toggles and momentary button switches.
If you want to do something similar you'll have to see dan's constant current LED driver circuit instructable.