Summary

Print your own fully functioning LED Flashlight!
(Electronics and batteries not included)
See jtfdailycheck.blogspot.com for more details
Disclaimer: The way I wired mine up ended up causing a short that ruined the batteries and melted the insulation on the wire! I made a few changes to the connections and it works fine. Please make sure your connections are very well insulated.

Instructions

All of the parts should be able to print without support. Mine has two perimeters and 20% infill.
The threading on the caps has some built in tolerance, so getting the parts to fit shouldn't be a problem - my printer isn't extremely accurate and they fit perfectly. I included the Solidworks files in case you would like to modify them.
Other Parts:
A small, approx. 7mm pushbutton
Up to 4 - 5mm LEDs (I used the 'High Brightness White LEDs' from Radioshack)
Some wire
A spring
A large nut
A 50mm diameter cut circle of acrylic (or something clear to protect the bulbs)
Hot Glue
2 AA batteries
Assembly:
1) Hot glue a wire in the main body of the light with about 2 inches of excess wire on either end. Make sure the wire is within the ribs.
2) Attach the button in the back cap and solder the wire onto one of the terminals.
3) Solder and hot glue the spring onto the back of the button. (I also soldered and hot glued a small nut on the other side of the spring for better contact with the battery terminal). See photo.
4) Hot glue and solder the LED's (in parallel) to the cone, making sure that one LED has its anode and cathode accessible for connections.
5) Solder the wire to one of the LED's terminals. You may want to mock this up with alligator clips to see which direction the batteries will have to point. Mine is set up with the negative terminal at the back with the switch, but it really shouldn't matter.
6) Hot glue the large nut to the back of the LED assembly (see photo) and pinch the other LED lead in between the hot glue and the nut, creating a contact for the battery. I used a small piece of metal here to expand the contact size and keep the glue from insulating the contact. You may need to get creative here...
7) Cut out a circular piece of acrylic about 50mm - 52mm in diameter. I used 3mm acrylic, but there is plenty of room in the cap for thicker acrylic if needed.
8) Enjoy!
Update: I ended up redoing the switch mechanism. I instead used a bolt and a spring. The bolt makes a contact with the back of the battery and is connected to the wire running to the LED's. It's a cool mod and doesn't require any special parts. It may be a little less reliable, but is much less likely to short.
Feel free to get creative on how to hook up the wiring!

4-LED 2-AA Flashlight