SMJLED is a 5mm LED and won't be nearly as bright as even a 1-Watt Luxeon. I wouldn't even bother with them. Ditto the Niteyes.
All of the following are true drop-ins. They can all be installed as easily as changing the stock bulb. Most of these products are reviewed on FlashlightReviews.com. See the link in the post above.
Diamond Luxeon I and Luxeon III drop-in modules are extremely bright, have excellent throw, require no modification, and are relatively inexpensive. They use the same Luxeon brand LEDs as most high-powered LED flashligts. The LuxIII module needs 3 batteries to work. If you replace one of your 4 batteries with a "dummy battery" and use a Lux III, your light will be lighter, and much brighter. There's no downside to using only 3 batteries, because the runtime will still be more than 24 hours with the Lux III. You can use a Lux I with your 2-cell Mag, and it will be brighter and throw better than the stock bulb, but nowhere near the brightness and throw of the Lux III
Diamond is also about to release the Luxeon K2 drop-in. It will work with up to 6-cell MagLites. It will almost certainly be even brighter than the Lux III drop-in and still cost only $24.95. It should produce at least 100 lumens. (The stock bulb in a 3-D cell Mag makes less than 30 lumens for comparison) If you can wait, buy that one. If not, buy the Diamond Lux III. You cant go wrong. Currently Diamond is offering blow-out pricing on their Lux III drop-ins. Just $19.95. See:
http://www.flash-lights.com/index.php/cat/c1243_3-Watt-Luxeon-LED-s.html/XTCsid/5b8bdbe933ad3af1e0ddde04e2417040
Here is a link to their K2 offer:
http://www.flash-lights.com/index.php/cat/c1305_6-5-Watt-Luxeon-K2.html
There are a couple other Luxeon drop-ins. EverLED makes a Luxeon drop-in but it isn't as bright as the Diamond LuxIII, and costs $39. LunaLEDs makes a 1 watt drop-in using a Cree brand emitter that is descent, but it is also around $39 and seems sketchy to me. At least, that is, their web site sucks. I couldn't even tell if they were taking orders for it.
In my opinion, your only decision shoud be which Diamond drop-in to buy. It's true that Mag industries is going to release their own brand of drop-ins very soon, but I don't have any reason to believe they will be as good as Diamond's Lux III or K2 drop-ins.
The K-2 in a 4-D cell Mag will be brighter and throw farther than almost any LED flashlight currently available. If you already have the 4-D Mag, you can own some true whup-*** for only $25 I don't know why you would do anything else. As stated earlier, if you can't wait, I don't know why you would choose anything but the Diamond Lux III for $20
Now go out and light up the neighborhood!
Bernie