The LED drop-in that I use in my Mag is the TerraLUX TLE-300; ~600 lumens at the emitter for $73:
http://www.batteryjunction.com/tle-300.html
It's essentially just three LEDs, each with its own optic, all in a self-contained drop-in puck with all the necessary circuitry. It's a minimal difficulty install, you remove the stock Mag reflector and bulb, put the TLE-300 in the socket, done.
Optic lenses mean *serious throw* and the TLE-300 doesn't disappoint, projecting a big fat hotspot with no corona or spill to speak of. You lose the Mag's focusing ability, but when you've got a glaring hotspot that's over two feet across from only ten feet away, you don't need it. The only con is that the hotspot looks a bit like a round, multi-pointed star (the optics to some degree project the square shape of the LEDs) but in normal use, especially outdoors, you don't notice it.
I mainly use my TLE-300 Mag on night walks down our suburb street to the area mailbox. Any time a car drives by going the same direction, it's a perfect side-by-side comparison of light output, and you can't miss it - the Mag is putting out just as much light as the car (the cars don't miss it either, as they usually slow down). It's still impressive every time I see it.
The TLE-300 is my fave Mag drop-in based on its ease of install, use of standard batteries, and good old "damn that's bright"-ness. I've always liked the idea of an LED hotwire/ROP that doesn't require any modding, and this certainly fills the bill.