i use trustfire protected rcr123 and 18650 cells. i preffer the 18650 cells.

my primary carry light is an ultrafire wf-501b (not the one from dxextreme as they only take cr123/rcr123 cells).

i get the cheap xenon bulb version off ebay and swap the dropin module for a P60 Q5 module also from ebay. with the 18650 cell the light is direct driven and gives outstanding run time of over 6 hours.

dx now stock P60 3 mode 0-100% Q5 modules and i have ordered one to see what they are like.

ultrafire flashlight
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=320211416095&ssPageName=STRK:MEWA:IT&ih=011

Q5 module
http://cgi.ebay.co.uk/Ultrafire-CREE-Q5-...1713.m153.l1262

Trustfire 18650
http://www.dealextreme.com/details.dx/sku.5790

for those of you that have never used a Lithium Battery and are thinking of doing so please be careful and do your homework before you get them. they work well but you have to respect them

http://www.candlepowerforums.com/vb/showthread.php?t=106242

never ever use unprotected cells