Mrd 74,
Since I use rechargeable AA's, I overdrive bulbs made for 3-alkaline cells for great brightness.
Currently, my favorite bulbs for this are the XPR3 Xenon lamps originally made for the Hubbellite 3003-C. Found 'em on clearance at Lowe's, 2 for 85 cents!
I'm using this in 4AA light from Big Lots which I believe is a close clone of the Turtlelight-I. It has the smooth reflector, and a very piercing narrow beam with the XPR3 Xenon lamp, and has nearly become my favorite inexpensive light for general use. The beam is nearly PERFECT with WriteWrite film on the lens.
Most 3-cell Krypton bulbs seem to stand up well to overdriving with 4AA's. Xenon's (if you can find 'em) tend to be a little more sensitive to overdriving, so I guess I've been lucky so far.
Good luck - John