Heres a few ideas:
LED OPTIONS - I have used a G&P 3W LED drop in. Just drops straight into the 6P. It is not bad and gives long runtime. Heres a review:
http://www.flashlightreviews.com/reviews/gp_p60lux3.htm
They can be bought from Bug out Gear, Lighthound or the cheapest is ebay ($31 USD delivered). Heres the guy I got mine from:
http://cgi.ebay.com.au/G-P-3W-LED-L...QQihZ017QQcategoryZ106987QQrdZ1QQcmdZViewItem
G&P also makes the same sort of thing in 1W led, 5W led and K2 Led (available from the same sellers as the 3W)
Incan - The Lumen Factory has a range of different lamps you could try (D26 6 series). If you change to rechargable batteries you then have more options like the D26 HO4 with a 17670 battery or some of the 9v series with 2 x 3.7v rechargables.
I prefer incan lamps to LED and am currently using the 3.7v lamp and 17670 battery from AW. It is much brighter that the p60 lamp and I don't have to buy batteries. Heres the link to that set up:
http://candlepowerforums.com/vb/showthread.php?t=127715
When this Lamp dies I will be trying the HO4 lamp from Lumen Factory as I have heard good things about it.
I understand what Mercop is suggesting about a tac light being run on primary cells only. I used to think that too but have recently changed my thoughts. Probably best left for another thread rather than hijacking this one. All I will say is that if you are prepared to try difffernt batteries it will also give you more choices of Lamps as well.
I hope this info is some help.
Cheers