Well, at under $40, I'd imagine the Nuwai Quantum III would be pretty tough to beat on the lower end of the price scale. And though I haven't actually seen one, the Quantum I would probably be very smilarly good for a few dollars less. If you don't might a longer light, the Inova XO is pretty cool for under $50.
On the higher end, I've looked over most of the info out there and haven't found what I'm looking for. The closest would be the Surefire L2 but I don't care for what it looks like at all. And I think it could be smaller. I'd like a 2x123 light, preferably just slightly smaller than the Inova X5T running a hard driven Lux 3 light that has at least two power settings. It would have a tailpiece that had two detended 'tighten down' points and then a clickie. The high power level would be about 80 lumens and the low would be about 5 lumens.