Here are two more threads comparing mods. My quickie opinion:
Opalec- most generally useful amount of light and 2x battery life vs. incandescent. Is as bright as the stock bulb once the batteries aren't spanking new. Warning light is cool. I don't know, but imagine the Terralux 4x5mm LED mod has similar output but no warning.
TerraLux - Easiest to put in, but not like any are a challenge. Good for alkaline batteries as the 300mA current input is reasonable. 8 hr runtime, brighter than stock bulb with new batteries.
Inretech- can't really recommend except with Lithium AA cells for an emergency light. It is cheaper than other luxeon mods though as no electronics. Also the most reliable. Will run off alkaline for a long time, but pretty dim generally, and doesn't fully discharge the batteries.
MadMax by Dat2zip - the adjustable or light (500mA input) versions are good if you want a lot of light but don't want to give up the option of alkalines. 500mA is overdoing it for alkaline AAs but the converter is very efficient and capable of running the batteries to 0.4V each. And, it's bright enough that you won't keep thinking your NiMHs should be in something that gives them a harder workout. Also available now in HD (longer throw, more uniform beam) for $30. The fraen optic is a little tight for general use but can be de-focused for a wider beam. Also, it's squirrely to fit it properly in the head, with the o-ring between it and the front lens, as it tends to slip through the middle of the "o". You can order a NX05 wider beam optic, which is best with a LD, but does work with a HD.
Lambda SMD+ - $25, Draws up to 2 amps, gets hot, picture is HD actual unit I got LD, dunno how hard it drives the LED. It's as bright as my Q3J MadMax adj set wide-open (WO), brighter than the MadMax lite HD I just got. The electronics or LED are not very efficient. Maybe as low as 60%. I can't find any measured efficiency or Iout spec - anyone know this info? Long and short of it is, this mod is for NiMH cells ONLY, and more tempting when the MadMax lite isn't on sale.
If that's not bright enough you're going to want a 3W LED on a BadBoy 750 or 1000, or Lambda's new 3W mod when they become generally available.
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=LED&Number=710178
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=LED&Number=710170