I agree with Art that if you've got a bunch of mini-mags the Niteize 1W upgrade is an inexpensive and sensible upgrade, and I recommend them to anyone who wants to get better performance and run-time from the flashlights they already own.

Nevertheless, I think you're selling yourself short if you don't investigate the better purpose-built LED lights currently on the market. In addition to about 1/2-dozen mini-mags I've upgraded with Niteize, I've got a Fenix L2D on my BOB, a Fenix L0D in the sheath of my Leatherman Charge AL in my EDC bag, and a Maratac AAA on my mini 'biner with a Leatherman Micra and my keys, all loaded with Eveready Lithium batteries. I also gave away Fenix E01's as gifts this Christmas.

Finally I've got two Petzl Zipka Plus 2 LED headlamps, (one in my BOB and one in my EDC bag), and two Coast dual-color LED headlamps with my camping gear.

Fenix L2D: Exceptionally bright (180 lumens) for a 2xAA light. Wish low was much lower, like 5 instead of 12 lumens, which would give a run-time of over 100 hours instead of 55. Complicated user interface: would prefer low-med-high-turbo without the blinking modes. Expensive at $60 at Amazon.

Fenix LD01: Amazing brightness from a single AAA (80 lumens) or over 8 hours at a very usable low (10 lumen) range. Simple twisty switch with med-low-high modes (no flashing modes). Frequently available for $36 from Amazon.com.

Fenix E01: 21 hour run time at 10 lumen (same brightness but 4x runtime as Niteize) from a single AAA. Simple on-off switching. $12 with free shipping from Amazon.com makes it only a few dollars more than the Niteize upgrade. But I don't like the stiff twisty switch or purple light output.

Maratac AAA: My absolute favorite. 1.5 lumens on low for 50 hours, 18 on medium for 4 hours or 50 minutes at 80 lumens on high. Easy to use twisty switch. Smallest light of the bunch. Low mode is great for seeing where you're walking, search through drawers/packs, reading menus. Best of all, at $22 it's very affordable. Only available on-line from countycomm.com.

Petzl Zipka Plus 2: I like these because they have good brightness on high and usable brightness but long run time on low, and they pack very small and light because they use a retractable cord instead of elastic band. They are reasonably comfortable and secure using the cord instead of the band, and I've used them during strenuous outdoors activities for hours without problem.

Coast Dual Color Headlamp: My first good LED headlamps bought at Costco (no longer sold there, I believe). I've had one for four years and it's still running great on the original set of batteries. I went diving with one once in an emergency, not deep -- 5-10 feet and only for 15 minutes -- and even though it's not advertised as being waterproof it worked fine and suffered no noticeable ill effects.