4D233,
Other have addressed your question pretty well in terms of super high output (i kid you not, the
M@g85 and ROP mentioned can toe to toe with car headlights). The downside of them are the expenses and very short runtime (compared to a normal stock
M@glite).
If you wanted something reliable with a good runtime, simply replace the bulbs with something of lower rated voltage. Eg with your 4D
M@g, pop a 3D bulb in there. It will run a fair bit brighter and bulb life is still pretty good. You can also fit "C" cells into your D instead and keep your current bulb, quite similar to the changing bulb method i mentioned. To use C cells, simply fit a rubber hose inside the light or wrapped paper, and fit one more extra cell than you would if you were using "D" cells. You'll have to change the tailcap spring so it sits upside as well, easy 2 second job.
The LED dropins are a good idea too. Brighter than the normal bulbs a fair bit, and if focused well, will out-throw the stock bulb setup too. And they're shockproof and never need replacing.
If want you wanted was a firestarter, refer to the
M@g85, ROP or 12V 100W hotwire that Missionaryman mentioned